# dev input variables¶

This document lists and provides the description of the name (keywords) of the dev input variables to be used in the input file for the abinit executable.

## builtintest¶

Mnemonics: BUIT-IN TEST number
Characteristics: DEVELOP
Mentioned in topic(s): topic_Control
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Moderately used, [14/998] in all abinit tests, [0/117] in abinit tutorials

When builtintest is non-zero, the input file is a special one, that runs very quickly, and that is accompanied by a specific analysis by ABINIT, at the end of the run, against a hard-coded value of total energy (and possibly stresses, forces …). The echo of the analysis is done in the STATUS file. In particular, such built-in tests can be used to check quickly whether ABINIT fallbacks have been connected or not (bigdft, etsf_io, libxc, wannier90). At present, builtintest = 1… 7 are allowed. See more information in tests/built-in/README.

## densfor_pred¶

Mnemonics: DENSity and FORces PREDictor
Characteristics: DEVELOP
Mentioned in topic(s): topic_SCFAlgorithms, topic_MolecularDynamics
Variable type: integer
Dimensions: scalar
Default value: 6 if paral_kgb == 1, 2 otherwise.

Only relevant if: iscf > 0

Test list (click to open). Moderately used, [37/998] in all abinit tests, [0/117] in abinit tutorials

Used when iscf > 0, to define:

• the way a change of density is derived from a change of atomic position,
• the way forces are corrected when the SCF cycle is not converged.

Supported values:

• 0 → density not changed (fixed charge), forces not corrected
• 1 → density not changed, forces corrected with rigid ion hypothesis (atomic charge moved with atom)
• 2 → density changed and forces corrected with rigid ion hypothesis (atomic charge moves with atom)
• 3 → density changed and forces corrected with a different implementation of the rigid ion hypothesis
• 4 → density not changed, forces corrected with the use of Harris functional formula (see note)
• 5 → density changed using D. Alfe 2nd-order algorithm (see notes), forces not corrected
• 6 → density changed using D. Alfe 2nd-order algorithm (see notes) and forces corrected with the use of Harris functional formula

Similar negative values are also allowed (see the meaning later), for development purposes only. No meaning for RF calculations.

For the time being,

concerning the correction of forces (use of densfor_pred = 1, 2, 3, 4 or 6)

The force on the atom located at R is corrected by the addition of the following term: $F_{residual}=\int dr V_{residual} \frac{d \rho_{atomic}}{dR}$, where $\rho_{atomic}$ is an atomic (spherical) density.

• When such an atomic density ($\rho_{atomic}$) is found in the pseudopotential or PAW file, it is used. If not, a gaussian density (defined by densty parameter) is used.
• When SCF mixing is done on the density (iscf >= 10), the potential residual ($V_residual$) is obtained from the density residual with the first order formula $V_{residual}=\frac{dV}{d \rho} \rho_{residual}$ and uses the exchange-correlation kernel $\frac{dV_{xc}}{d\rho}=K_{xc}$ whose computation is time-consuming for GGA functionals. By default (positive values of densfor_pred), the local- density part of the GGA exchange-correlation kernel is used (even for GGA, for which it seems to give a reasonable accuracy). Using the full GGA exchange correlation kernel (so, including derivatives with respect to the gradient of the density) is always possible by giving a negative value to densfor_pred. In case of hybrid functionals, a similar correction term is added, although in the density mixing scheme, the related GGA kernel is used instead of the hybrid functional kernel.

concerning the use of densfor_pred = 5 or 6 (density prediction)

The algorithm is described in [Alfe1999]. It uses an atomic (spherical) density. When such an atomic density is found in the pseudopotential or PAW file, it is used. If not, a gaussian density (defined by densty parameter) is used. Also note that, to be efficient, this algorithm requires a minimum convergence of the SCF cycle; Typically, vres2 (or nres2) has to be small enough (10 -4 …10 -5 ).

## densty¶

Mnemonics: initial DENSity for each TYpe of atom
Characteristics: DEVELOP
Mentioned in topic(s): topic_xc
Variable type: real
Dimensions: (ntypat)
Default value: 0.0

Test list (click to open). Moderately used, [33/998] in all abinit tests, [0/117] in abinit tutorials

Gives a rough description of the initial GS density, for each type of atom. This value is only used to create the first exchange and correlation potential, and is not used anymore afterwards. For the time being, it corresponds to an average radius (a.u.) of the density, and is used to generate a gaussian density. If set to 0.0d0, an optimized value is used. No meaning for RF calculations.

Mnemonics: Dynamical Mean Field Theory: READ OCCupations (Non Diagonal)
Characteristics: DEVELOP
Mentioned in topic(s): topic_DMFT
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [5/998] in all abinit tests, [0/117] in abinit tutorials

Flag to read/write Occupations as computed in DMFT. This flag is useful to restart a DFT+DMFT calculation with self-consistency over electronic density. The occupations are written each time a DMFT loop is finished. So if the calculation stops because the time limit is reached, this option offers the possibility to restart the self-consistent loop over density at the point where it stopped (assuming a restart with the wave functions, see getwfk).

• 0 → Occupations are written but never read.
• 1 → Occupations are read from I_DMFTOCCND, where I is the root for input files.
• 2 → Occupations are read from O_DMFTOCCND, where O is the root for output files.

An alternative and more simple way to restart a DFT+DMFT calculation is to use the density file (obtained with prtden = 1 or prtden = -1) and the self-energy (see dmft_rslf).

## dmftctqmc_basis¶

Mnemonics: Dynamical Mean Field Theory: Continuous Time Quantum Monte Carlo BASIS
Characteristics: DEVELOP
Mentioned in topic(s): topic_DMFT
Variable type: integer
Dimensions: scalar
Default value: 1
Only relevant if: dmft_solv == 5

Test list (click to open). Rarely used, [4/998] in all abinit tests, [0/117] in abinit tutorials

Choose the basis to perform CTQMC calculation.

• 0 → Use the local basis in the spherical harmonics basis. Can be useful if the Hamiltonian has weak off diagonal terms and for this reason, one want to keep the original basis for simplicity and for physical insight.
• 1 → Default value, diagonalize the local Hamiltonian (but only if it is not diagonal). The best choice in general.
• 2 → Diagonalise the local correlated occupation matrix. Can lead to non diagonal Hamiltonian that cannot be handled by CTQMC. This option should be thus avoided.

## effmass_free¶

Mnemonics: EFFective MASS for the FREE electron
Characteristics: DEVELOP
Mentioned in topic(s): topic_Artificial
Variable type: real
Dimensions: scalar
Default value: 1

Test list (click to open). Rarely used, [3/998] in all abinit tests, [0/117] in abinit tutorials

This parameter allows one to change the free electron mass, with respect to its experimental value. The electron mass is simply changed in the Schrodinger equation. Only for testing purposes, of course.

## eshift¶

Mnemonics: Energy SHIFT
Characteristics: DEVELOP, ENERGY
Mentioned in topic(s): topic_SCFAlgorithms
Variable type: real
Dimensions: scalar
Default value: 0
Only relevant if: wfoptalg == 3

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

eshift gives the shift of the energy used in the shifted Hamiltonian squared. The algorithm will determine eigenvalues and eigenvectors centered on eshift. Can be specified in Ha (the default), Ry, eV or Kelvin, since eshift has the ‘ENERGY‘ characteristics. (1 Ha=27.2113845 eV)

## exchmix¶

Mnemonics: EXCHange MIXing
Characteristics: DEVELOP
Mentioned in topic(s): topic_xc
Variable type: real
Dimensions: scalar
Default value: 0.25
Only relevant if: useexexch == 1

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

exchmix allows one to tune the ratio of exact exchange when useexexch is used. The default value of 0.25 corresponds to PBE0.

## exchn2n3d¶

Mnemonics: EXCHange N2 and N3 Dimensions
Characteristics: DEVELOP
Mentioned in topic(s): topic_TuningSpeed
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

If exchn2n3d is 1, the internal representation of the FFT arrays in reciprocal space will be array(n1,n3,n2), where the second and third dimensions have been switched. This is to allow to be coherent with the exchn2n3d = 4xx FFT treatment.

## extrapwf¶

Mnemonics: flag - EXTRAPolation of the Wave-Functions
Characteristics: DEVELOP
Mentioned in topic(s): topic_TuningSpeed, topic_MolecularDynamics
Variable type: integer
Dimensions: scalar
Default value: 0
Only relevant if: densfor_pred in [5, 6]

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

This flag activates the extrapolation of wave-functions from one Molecular Dynamics (or Structural Relaxation) step to another. The wave functions are extrapolated using 2nd-order algorithm of [Arias1992]. Note that, when activated, this extrapolation requires non-negligible additional memory resources as the wave functions are stored for the two previous time steps. Also, it can only be activated if a consistent density extrapolation is activated (see densfor_pred). ABINIT 7.10: this option is under development and might give wrong results.

## fermie_nest¶

Mnemonics: FERMI Energy for printing the NESTing function
Mentioned in topic(s): topic_printing
Variable type: real
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [3/998] in all abinit tests, [0/117] in abinit tutorials

This input variable is only effective when prtnest = 1. The energy is relative to the calculated Fermi energy.

## fftalg¶

Mnemonics: Fast Fourier Transform ALGorithm
Characteristics: DEVELOP
Mentioned in topic(s): topic_TuningSpeed
Variable type: integer
Dimensions: scalar
Default value: 312 if FFTW3 and usedmft == 0, 401 if paral_kgb == 1, 112 otherwise.

Test list (click to open). Moderately used, [34/998] in all abinit tests, [1/117] in abinit tutorials

This keyword is irrelevant when Fast Fourier Transforms are done using Graphics Processing Units (GPU), i.e. when use_gpu_cuda = 1 (in that case, it is ignored).

Allows to choose the algorithm for Fast Fourier Transforms. These have to be used when applied to wavefunctions (routine src/53_ffts/fourwf.F90), as well as when applied to densities and potentials (routine src/53_ffts/fourdp.F90). Presently, it is the concatenation of three digits, labelled (A), (B) and (C).

The first digit (A) is to be chosen among 1, 2, 3, 4 or 5:

• 1 → use FFT routines written by S. Goedecker.
• 2 → not available anymore
• 3 → use serial or multi-threaded FFTW3 fortran routines (http://www.fftw.org ). Currently implemented with fftalg = 312.
• 4 → use FFT routines written by S. Goedecker, 2002 version, that will be suited for MPI and OpenMP parallelism.
• 5 → use serial or multi-threaded MKL routines Currently implemented with fftalg = 512.

The second digit (B) is related to src/53_ffts/fourdp.F90:

• 0 → only use Complex-to-complex FFT
• 1 → real-to-complex is also allowed (only coded for A==1, A==3 and A==5)

The third digit (C) is related to src/53_ffts/fourwf.F90:

• 0 → no use of zero padding
• 1 → use of zero padding (only coded for A==1, A==4)
• 2 → use of zero padding, and also combines actual FFT operations (using 2 routines from S. Goedecker) with important pre- and post-processing operations, in order to maximize cache data reuse. This is very efficient for cache architectures. (coded for A==1 and A==4, but A==4 is not yet sufficiently tested)

Internal representation as ngfft(7).

## fftcache¶

Mnemonics: Fast Fourier Transform CACHE size
Characteristics: DEVELOP
Mentioned in topic(s): topic_TuningSpeed
Variable type: integer
Dimensions: scalar
Default value: 16
Comment: todo: Not yet machine-dependent

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

Gives the cache size of the current machine, in Kbytes. Internal representation as ngfft(8).

## getgam_eig2nkq¶

Mnemonics: GET the GAMma phonon data EIG2NKQ from dataset
Mentioned in topic(s): topic_multidtset, topic_TDepES
Variable type: integer
Dimensions: scalar
Default value: 0
Only relevant if: ieig2rf != 0 and qpt != (0.0, 0.0, 0.0)

Test list (click to open). Rarely used, [2/998] in all abinit tests, [0/117] in abinit tutorials

Relevant for second-order eigenvalue calculations using response-functions (ieig2rf != 0), and only for non-zero wavevectors qpt. From the electron-phonon matrix elements at some wavevector only, it is not possible to determine the Debye-Waller contribution: one has to know also the q=Gamma electron-phonon matrix elements. The variable getgam_eig2nkq allows one to transmit the information about the second-order derivatives of the eigenvalues for q=Gamma from the dataset where the calculation at Gamma was done, to the datasets for other wavevectors.

## getwfkfine¶

Mnemonics: GET the fine grid wavefunctions from _WFK file
Mentioned in topic(s): topic_multidtset, topic_DFPT, topic_TDepES
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [6/998] in all abinit tests, [0/117] in abinit tutorials

Eventually used when ndtset > 0 (in the multi-dataset mode), to indicate starting wavefunctions, as an alternative to irdwfkfine. One should first read the explanations given for these latter variables. The getwfkfine variables is typically used to chain the calculations in the multi-dataset mode, since they describe from which dataset the OUTPUT wavefunctions are to be taken, as INPUT wavefunctions of the present dataset. If getwfkfine == 0, no use of previously computed output wavefunction file appended with _DSx_WFK is done. If getwfkfine is positive, its value gives the index of the dataset for which the output wavefunction file appended with _WFK must be used. If getwfkfine is -1, the output wf file with _WFK of the previous dataset must be taken, which is a frequently occurring case. If getwfkfine is a negative number, it indicates the number of datasets to go backward to find the needed wavefunction file. In this case, if one refers to a non existent data set (prior to the first), the wavefunctions are not initialised from a disk file, so that it is as if getwfkfine = 0 for that initialisation. Thanks to this rule, the use of getwfkfine -1 is rather straightforward: except for the first wavefunctions, that are not initialized by reading a disk file, the output wavefunction of one dataset is input of the next one. NOTE: a negative value of a “get” variable indicates the number of datasets to go backwards; it is not the number to be subtracted from the current dataset to find the proper dataset. As an example:

 ndtset 3   jdtset 1 2 4  getXXX -1


refers to dataset 2 when dataset 4 is initialized. Response-function calculation:

• one and only one of getwfkfine or irdwfkfine MUST be non-zero
• if getwfkfine = 1: read ground state k -wavefunctions from a disk file appended with _WFK, produced in a previous ground state calculation.
• Reading the fine grid wavefunction will trigger the k-points interpolation technique of the temperature dependent calculations.

Bethe-Salpeter calculation:

For further information about the files file, consult the abinit help file.

This variable is experimental. In development.

## intxc¶

Mnemonics: INTerpolation for eXchange-Correlation
Characteristics: DEVELOP
Mentioned in topic(s): topic_xc
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Moderately used, [148/998] in all abinit tests, [1/117] in abinit tutorials
• 0 → do “usual” xc quadrature on fft grid
• 1 → do higher accuracy xc quadrature using fft grid and additional points at the centers of each cube (doubles number of grid points)–the high accuracy version is only valid for boxcut>=2. If boxcut < 2, the code stops.

For RF calculations only intxc = 0 is allowed yet. Moreover, the GS preparation runs (giving the density file and zero-order wavefunctions) must be done with intxc = 0

Prior to ABINITv2.3, the choice intxc = 1 was favoured (it was the default), but the continuation of the development of the code lead to prefer the default intxc = 0. Indeed, the benefit of intxc = 1 is rather small, while making it available for all cases is a non-negligible development effort. Other targets are prioritary… You will notice that many automatic tests use intxc = 1. Please, do not follow this historical choice for your production runs.

## iomode¶

Mnemonics: Input-Output MODE
Characteristics: DEVELOP
Mentioned in topic(s): topic_parallelism
Variable type: integer
Dimensions: scalar
Default value: 1 if MPI_IO and paral_kgb == 1, 0 otherwise.

Test list (click to open). Moderately used, [29/998] in all abinit tests, [0/117] in abinit tutorials

This option selects the format used to produce the output wavefunction files and the files containing densities and potentials. It mainly affects the creation of the output files since several parts of Abinit are able to read data from files independently of their format (either binary files or netcdf files). The possible values are:

• 0 → Use standard Fortran IO (ok for sequential runs, not suitable for large parallel runs)
• 1 → Use MPI/IO routines (ok both for sequential and large parallel runs)
• 3 → Use NetCDF library to produce files according to the ETSF specification [Gonze2008] (ok for sequential, requires netcdf4 + hdf5 + MPI-IO support for large parallel runs)

By default, Abinit produces Fortran files and uses parallel MPI-IO under the hood when these operations cannot be implemented in terms of simple Fortran write/read statements. For example, paral_kgb = 1 uses the MPI-IO API provided by your MPI library.

In a nutshell, use the default value and make sure that your MPI library supports MPI-IO before embarking yourself in large parallel runs (HAVE_MPI_IO should be set to 1 in ~abinit/config.h). Many MPI libraries, nowadays, support the MPI-2 standard so it’s very likely that your MPI supports parallel IO. If you encounter problems, please ask your sysadmin to install a MPI library with MPI-IO capabilities.

There are cases, however, in which you would like to change the default behaviour. For example, you may want to generate WFK or DEN files in etsf-io format because you need data in this format. In this case, you have to use iomode==3 in the input file to override the default behaviour. Note however that you still need parallel IO capabilities enabled in the netcdf library if you want to produce netcdf files in parallel with paral_kgb = 1 (i.e. netcdf4 + hdf5 + MPI-IO). At present, the internal fallbacks provided by Abinit do not support netcdf4 so you have to link against an external netcdf library that supports hdf5+MPI-IO and is compatible with the mpif90 used to compile Abinit. See ~abinit/doc/build/config-examples/ubu_gnu_4.9_mpich.ac for a typical configuration file.

Additional note : The use of the ETSF_IO library [Caliste2008] has been disabled, and replaced by direct NetCDF calls. The ETSF_IO library was indeed not maintained anymore.

## iprcfc¶

Mnemonics: Integer for PReConditioner of Force Constants
Characteristics: DEVELOP
Mentioned in topic(s): topic_GeoOpt
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [4/998] in all abinit tests, [0/117] in abinit tutorials

Used when iscf > 0, to define the SCF preconditioning scheme. Potential- based preconditioning schemes for the SCF loop are still under development. The present parameter (force constant part) describes the way a change of force is derived from a change of atomic position. Supported values:

• 0 → hessian is the identity matrix
• 1 → hessian is 0.5 times the identity matrix
• 2 → hessian is 0.25 times the identity matrix
• -1 → hessian is twice the identity matrix *… (simply corresponding power of 2 times the identity matrix)

No meaning for RF calculations.

## irandom¶

Mnemonics: Integer for the choice of the RANDOM number generator
Characteristics: DEVELOP
Mentioned in topic(s): topic_PIMD
Variable type: integer
Dimensions: scalar
Default value: 3

Test list (click to open). Rarely used, [2/998] in all abinit tests, [0/117] in abinit tutorials

For the time being, only used when imgmov = 9 (Langevin Path-Integral Molecular Dynamics). irandom defines the random number generator.

Supported values:

• 1 → “uniformrandom”, delivered with ABINIT package (initially comes from numerical recipes).
• 2 → intrinsic Fortran 90 random number generator.
• 3 → “ZBQ” non-deterministic random number generator by R. Chandler and P. Northrop. Documentation and Source code

irandom = 3 is strongly advised when performing Molecular Dynamics restarts (avoids bias).

## irdwfkfine¶

Mnemonics: Integer that governs the ReaDing of the grid _WFK file on the FINE grid
Mentioned in topic(s): topic_multidtset, topic_TDepES
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

Indicates eventual starting wavefunctions. As alternative, one can use the input variables getwfkfine.

Ground-state calculation:

Response-function calculation:

• one and only one of irdwfkfine or getwfkfine MUST be non-zero
• if irdwfkfine = 1: read ground state k -wavefunctions from a disk file appended with _WFK, produced in a previous ground state calculation
• Reading the fine grid wavefunction will trigger the k-points interpolation technique of the temperature dependent calculations.

Bethe-Salpeter calculation:

For further information about the files file, consult the abinit help file.

This variable is experimental. In development.

## isecur¶

Mnemonics: Integer for level of SECURity choice
Characteristics: DEVELOP
Mentioned in topic(s): topic_SCFAlgorithms
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [9/998] in all abinit tests, [0/117] in abinit tutorials

In the presently used algorithms, there is a compromise between speed and robustness, that can be tuned by using isecur. If isecur =0, an extrapolation of out-of-line data is allowed, and might save one non-SCF calculation every two line minimisation when some stability conditions are fulfilled (since there are 2 non-SCF calculations per line minimisation, 1 out of 4 is saved) Using isecur = 1 or higher integers will raise gradually the threshold to make extrapolation. Using isecur = -2 will allow to save 2 non-SCF calculations every three line minimisation, but this can make the algorithm unstable. Lower values of isecur allows one for more (tentative) savings. In any case, there must be one non-SCF computation per line minimisation. No meaning for RF calculations yet.

## istatr¶

Mnemonics: Integer for STATus file rate
Characteristics: DEVELOP, NO_MULTI
Mentioned in topic(s): topic_printing
Variable type: integer
Dimensions: scalar
Default value: 0
Comment: Values lower than 10 may not work on some machines.

Test list (click to open). Moderately used, [14/998] in all abinit tests, [0/117] in abinit tutorials

Govern the rate of output of the status file. This status file is written when the number of the call to the status subroutine is equal to istatshft modulo istatr, so that it is written once every istatr call. When istatr = 0, there is no writing of a status file (which is the default).

## istatshft¶

Mnemonics: Integer for STATus file SHiFT
Characteristics: DEVELOP, NO_MULTI
Mentioned in topic(s): topic_printing
Variable type: integer
Dimensions: scalar
Default value: 1

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

Govern the rate of output of the status file. This status file is written when the number of the call to the status subroutine is equal to ‘istatshft‘ modulo ‘ istatr ‘, so that it is written once every ‘ istatr ‘ call. There is also a writing for each of the 5 first calls, and the 10th call.

## istwfk¶

Mnemonics: Integer for choice of STorage of WaveFunction at each k point
Mentioned in topic(s): topic_k-points, topic_TuningSpeed
Variable type: integer
Dimensions: (nkpt)
Default value: 0
*Comment:
For RF calculations, the Default is not used: istwfk is forced to be 1 deep inside the code, for all k points. For spin-orbit calculations (nspinor = 2), istwfk is also forced to be 1, for all k points.

Test list (click to open). Moderately used, [247/998] in all abinit tests, [32/117] in abinit tutorials

Control the way the wavefunction for each k-point is stored inside ABINIT, in reciprocal space. For the GS calculations, in the “cg” array containing the wavefunction coefficients, there is for each k-point and each band, a segment cg(1:2,1:npw). The ‘full’ number of plane wave is determined by ecut.

However, if the k-point coordinates are build only from zeroes and halves (see list below), the use of time-reversal symmetry (that connects coefficients) has been implemented, in order to use real-to-complex FFTs (see fftalg), and to treat explicitly only half of the number of plane waves (this being used as ‘npw’). For the RF calculations, there is not only the “cg” array, but also the “cgq” and “cg1” arrays. For the time-reversal symmetry to decrease the number of plane waves of these arrays, the q vector MUST be (0 0 0). Then, for each k point, the same rule as for the RF can be applied. WARNING (991018): for the time being, the time-reversal symmetry cannot be used in the RF calculations.

• 1 → do NOT take advantage of the time-reversal symmetry
• 2 → use time-reversal symmetry for k=( 0 0 0 )
• 3 → use time-reversal symmetry for k=(½ 0 0 )
• 4 → use time-reversal symmetry for k=( 0 0 ½)
• 5 → use time-reversal symmetry for k=(½ 0 ½)
• 6 → use time-reversal symmetry for k=( 0 ½ 0 )
• 7 → use time-reversal symmetry for k=(½ ½ 0 )
• 8 → use time-reversal symmetry for k=( 0 ½ ½)
• 9 → use time-reversal symmetry for k=(½ ½ ½)
• 0 → (preprocessed) for each k point, choose automatically the appropriate time-reversal option when it is allowed, and chose istwfk = 1 for all the other k points.

## lotf_classic¶

Mnemonics: LOTF CLASSIC model for glue model
Characteristics: DEVELOP
Mentioned in topic(s): topic_LOTF
Variable type: integer
Dimensions: scalar
Default value: 5

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

Glue model used in LOTF. For the moment it is imposed to be 5.

## lotf_nitex¶

Mnemonics: LOTF Number of ITerations
Characteristics: DEVELOP
Mentioned in topic(s): topic_LOTF
Variable type: integer
Dimensions: scalar
Default value: 10

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

Set the number of Molecular Dynamics iterations which are computed by LOTF.

## lotf_nneigx¶

Mnemonics: LOTF max Number of NEIGhbours
Characteristics: DEVELOP
Mentioned in topic(s): topic_LOTF
Variable type: integer
Dimensions: scalar
Default value: 5

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

Set the max number of Neighbours used in the LOTF method. For the moment it is imposed to be 40.

## lotf_version¶

Mnemonics: LOTF VERSION of MD algorithm
Characteristics: DEVELOP
Mentioned in topic(s): topic_LOTF
Variable type: integer
Dimensions: scalar
Default value: 2

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

Set the MD algorithm in the LOTF method. For the moment it is imposed to be 2.

## macro_uj¶

Mnemonics: MACRO variable that activates the determination of the U and J parameter (for the PAW+U calculations)
Characteristics: DEVELOP
Mentioned in topic(s): topic_DFT+U
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [4/998] in all abinit tests, [2/117] in abinit tutorials

Sets proper input values for the determination of U and J i.e. for pawujat (first atom treated with PAW+U), irdwfk (=1), tolvrs (=10^(-8)), nstep (=255), diemix (=0.45), atvshift (pawujat) pawujv). Do not overwrite these variables manually unless you know what you are doing.

• macro_uj = 1 (and nsppol = 2) Standard procedure to determine U on atom pawujat through a shift of the potential on both spin channels.
• macro_uj = 1 (and nsppol = 1) Non standard procedure to determine U from potential shift on atom pawujat (experimental).
• macro_uj = 2 (and nsppol = 2) Non standard procedure to determine U from potential shift on atom pawujat through a shift on spin channel 1 on this atom and the response on this channel (experimental).
• macro_uj = 3 (and nsppol = 2) Standard procedure to determine J from potential shift on spin channel 1 on atom pawujat and response on spin channel 2 (experimental).

Determination of U and J can be done only if the symmetry of the atomic arrangement is reduced and the atom pawujat is not connected to any other atom by symmetry relations (either input reduced symmetries manually, define concerned atom as a separate atomic species or shift concerned atom from ideal position).

## maxnsym¶

Mnemonics: MAXimum Number of SYMetries
Characteristics: DEVELOP
Mentioned in topic(s): topic_crystal
Variable type: integer
Dimensions: scalar
Default value: 384

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

Gives the maximum number of spatial symetries allowed in the memory. The default value is sufficient for most applications. It might have to be increased in the case of the use of a supercell (unit cell identically repeated).

## mem_test¶

Mnemonics: MEMory TEST
Characteristics: DEVELOP
Mentioned in topic(s): topic_Control
Variable type: integer
Dimensions: scalar
Default value: 1

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

This variable controls the memory test done in the memana routine. Possible values:

• 0 no test on the available memory is performed
• 1 the routine tries to allocate the estimated memory, for testing purposes, and if a failure occurs, the routine stops.
• 2 like 1, but before stopping, the routine will provide an estimation of the available memory.

## mqgrid¶

Mnemonics: Maximum number of Q-space GRID points for pseudopotentials
Characteristics: DEVELOP
Mentioned in topic(s): topic_Planewaves
Variable type: integer
Dimensions: scalar
Default value: 3001

Test list (click to open). Rarely used, [7/998] in all abinit tests, [0/117] in abinit tutorials

Govern the size of the one-dimensional information related to pseudopotentials, in reciprocal space: potentials, or projector functions.

## nbdblock¶

Mnemonics: Number of BanDs in a BLOCK
Characteristics: DEVELOP
Mentioned in topic(s): topic_TuningSpeed
Variable type: integer
Dimensions: scalar
Default value: 1

Test list (click to open). Rarely used, [2/998] in all abinit tests, [0/117] in abinit tutorials

In case of non-standard, blocked algorithms for the optimization of the wavefunctions (that is, if wfoptalg = 4):

## nc_xccc_gspace¶

Mnemonics: Norm-Conserving pseudopotentials - use XC Core-Correction in G-SPACE
Characteristics: DEVELOP
Mentioned in topic(s): topic_Planewaves
Variable type: integer
Dimensions: scalar
Default value: 0 if %usepaw == 0, 1 if %usepaw == 1, 0 otherwise.

Comment: 0 when %usepaw = 0, 1 when %usepaw = 1

Test list (click to open). Rarely used, [2/998] in all abinit tests, [0/117] in abinit tutorials

Historically, Abinit treats the model core charge used for the non-linear core correction in real space. Alternatively, it is possible to instruct the code to compute the core charge in G-space following the same approach used in the PAW code. The G-space formalism is more accurate than the interpolation in real space, especially when derivatives of the model core charge are needed, e.g. DFPT. Preliminary tests showed that the violation of the acoustic sum rule is reduced when nc_xccc_gspace == 1, especially for LDA. It is worth stressing, however, that nc_xccc_gspace == 1 should be used only in conjunction with NC pseudos whose model core charge that decays quickly in G-space. Several NC pseudos available in the Abinit table are not optimized for the G-space formalism and users are strongly invited to perform convergence studies with respect to ecut before using this option.

## nctime¶

Mnemonics: NetCdf TIME between output of molecular dynamics informations
Characteristics: DEVELOP
Mentioned in topic(s): topic_MolecularDynamics
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [2/998] in all abinit tests, [0/117] in abinit tutorials

When nctime is non-zero, the molecular dynamics information is output in NetCDF format, every nctime time step. Here is the content of an example file:

    netcdf md32.outH_moldyn1 {
dimensions:
time = UNLIMITED; // (11 currently)
DimTensor = 6;
DimCoord = 3;
NbAtoms = 32;
DimVector = 3;
DimScalar = 1;
variables:
double E_pot(time);
E_pot:units = "hartree";
double E_kin(time);
E_kin:units = "hartree";
double Stress(time, DimTensor);
Stress:units = "hartree/Bohr^3";
double Position(time, DimCoord, NbAtoms);
Position:units = "Bohr";
double Celerity(time, DimCoord, NbAtoms);
Celerity:units = "Bohr/(atomic time unit)";
double PrimitiveVector1(DimVector);
double PrimitiveVector2(DimVector);
double PrimitiveVector3(DimVector);
double Cell_Volume(DimScalar);
Cell_Volume:units = "Bohr^3";
}


## nloc_alg¶

Mnemonics: Non LOCal ALGorithm
Characteristics: DEVELOP
Mentioned in topic(s): topic_TuningSpeed
Variable type: integer
Dimensions: scalar
Default value: 4

Test list (click to open). Rarely used, [5/998] in all abinit tests, [0/117] in abinit tutorials

Allows to choose the algorithm for non-local operator application. On super- scalar architectures, the default nloc_alg = 4 is the best. More detailed explanations:

• nloc_alg = 2: Should be efficient on vector machines. It is indeed the fastest algorithm for the NEC, but actual tests on Fujitsu machine did not gave better performances than the other options.
• nloc_alg = 3: same as nloc_alg == 2, but the loop order is inverted.
• nloc_alg = 4: same as nloc_alg == 3, but maximal use of registers has been coded. This should be especially efficient on scalar and super-scalar machines. This has been confirmed by tests.

Note: internally, nloc_alg is stored in dtset%nloalg(1). See also nloc_mem for the tuning of the memory used in the non-local operator application.

## nloc_mem¶

Mnemonics: Non LOCal MEMOry
Characteristics: DEVELOP
Mentioned in topic(s): topic_TuningSpeed
Variable type: integer
Dimensions: scalar
Default value: 2 if %usepaw == 1, 1 otherwise.

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

Controls the memory use for the application of the non-local operator. More detailed explanations:

• nloc_mem == 1: (k+G) vectors are not precomputed, in order to save memory space.
• nloc_mem == 2: (k+G) vectors are precomputed, once per k-point.
• nloc_mem == -1 or -2: Negative values of nloc_mem correspond positive ones, where the phase precomputation has been suppressed, in order to save memory space, as an array double precision: ph3d(2,npw,[[natom]]) is saved (typically half the space needed for the wavefunctions at 1 k point - this corresponds to the silicon case). However, the computation of phases inside nonlop is somehow time-consuming.

Note: internally, sign(nloc_mem) is stored in dtset%nloalg(2) and abs(nloc_mem)-1 is stored in dtset%nloalg(3). See also nloc_alg for the algorithm for the non-local operator application.

## nnsclo¶

Mnemonics: Number of Non-Self Consistent LOops
Characteristics: DEVELOP
Mentioned in topic(s): topic_SCFControl
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Moderately used, [45/998] in all abinit tests, [2/117] in abinit tutorials

Gives the maximum number of non-self-consistent loops of nline line minimisations, in the SCF case (when iscf >0). In the case iscf <=0, the number of non-self-consistent loops is determined by nstep.

* The Default value of 0 -- for standard plane-wave calculations -- corresponds
to make the two first fixed potential determinations of wavefunctions have 2
non-self consistent loops, and the next ones to have only 1 non-self
consistent loop.

* The Default value of 0 -- for wavelets calculations ([[usewvl]] = 1) --
corresponds to make 2 steps with 3 non-self consistent loops, 2 steps with 2
non-self consistent loops, then the next ones with 1 non-self consistent loop.


## nnsclohf¶

Mnemonics: Number of Non-Self Consistent LOops for (Hartree)-Fock exact exchange
Characteristics: DEVELOP
Mentioned in topic(s): topic_Hybrids
Variable type: integer
Dimensions: scalar
Default value: 1 if %usefock == 1, 0 otherwise.

Test list (click to open). Rarely used, [6/998] in all abinit tests, [0/117] in abinit tutorials

Gives the maximum number of loops with non-self-consistent occupied states used to calculate Fock exact exchange, in the SCF case. The Default value is 0 when %usefock = 0. Default value is 1 when %usefock = 1 and correspond to update occupied wavefunctions at each self- consistent loop.

## normpawu¶

Mnemonics: NORMalize atomic PAW+U projector
Characteristics: DEVELOP
Mentioned in topic(s): topic_DFT+U
Variable type: integer
Dimensions: (ntypat)
Default value: 0

Test list (click to open). Rarely used, [0/998] in all abinit tests, [0/117] in abinit tutorials

Defines whether the atomic wave function (used as projectors in PAW+U) should be renormalized to 1 within PAW sphere.

## npulayit¶

Mnemonics: Number of PULAY ITerations for SC mixing
Characteristics: DEVELOP
Mentioned in topic(s): topic_SCFAlgorithms
Variable type: integer
Dimensions: scalar
Default value: 7
Only relevant if: iscf in [7,17]

Test list (click to open). Moderately used, [12/998] in all abinit tests, [1/117] in abinit tutorials

Gives the number of previous iterations involved in Pulay mixing (mixing during electronic SC iterations).

## nscforder¶

Mnemonics: Nth - SCaling Function ORDER
Mentioned in topic(s): topic_Coulomb
Variable type: integer
Dimensions: scalar
Default value: 16

Test list (click to open). Moderately used, [22/998] in all abinit tests, [0/117] in abinit tutorials

This variable controls the order of used scaling functions when the Hartree potential is computed using the Poisson solver (see icoulomb input variable). This variable is of seldom use since the default value is large enough. Nonetheless, possible values are 8, 14, 16, 20, 24, 30, 40, 50, 60, 100. Values greater than 20 are included in ABINIT for test purposes only.

## optforces¶

Mnemonics: OPTions for the calculation of FORCES
Characteristics: DEVELOP
Mentioned in topic(s): topic_ForcesStresses
Variable type: integer
Dimensions: scalar
Default value: 1 if toldff or tolrff != 0, 2 otherwise.

Test list (click to open). Moderately used, [51/998] in all abinit tests, [17/117] in abinit tutorials

Allows to choose options for the calculation of forces.

• optforces = 0: the forces are set to zero, and many steps of the computation of forces are skipped
• optforces = 1: calculation of forces at each SCF iteration, allowing to use forces as criterion to stop the SCF cycles
• optforces = 2: calculation of forces at the end of the SCF iterations (like the stresses)

## optnlxccc¶

Mnemonics: OPTion for the calculation of Non-Linear eXchange-Correlation Core Correction
Characteristics: DEVELOP
Mentioned in topic(s): topic_xc
Variable type: integer
Dimensions: scalar
Default value: 1

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

Allows to choose options for the calculation of non-linear XC correction. At present, only relevant for the FHI type of pseudopotentials, with pspcod=6.

• optnlxccc = 1: uses the old psp6cc.f routine, with inconsistent treatment of real-space derivatives of the core function (computed in this routine, while splined in the other parts of the code)
• optnlxccc = 2: consistent calculation derivatives, in the psp6cc_dhr.f routine from DHamann.

## ortalg¶

Mnemonics: ORThogonalisation ALGorithm
Characteristics: DEVELOP
Mentioned in topic(s): topic_TuningSpeed
Variable type: integer
Dimensions: scalar
Default value: -2 if wfoptalg >= 10 , 2 otherwise.

Test list (click to open). Moderately used, [12/998] in all abinit tests, [0/117] in abinit tutorials

Allows to choose the algorithm for orthogonalisation. Positive or zero values make two projections per line minimisation, one before the preconditioning, one after. This is the clean application of the band-by- band CG gradient for finding eigenfunctions. Negative values make only one projection per line minimisation. The orthogonalisation step is twice faster, but the convergence is less good. This actually calls to a better understanding of this effect. ortalg = 0, 1 or -1 is the conventional coding. ortalg = 2 or -2 try to make better use of existing registers on the particular machine one is running. More demanding use of registers is provided by ortalg = 3 or -3, and so on. The maximal value is presently 4 and -4. Tests have shown that ortalg = 2 or -2 is suitable for use on the available platforms.

## papiopt¶

Mnemonics: PAPI OPTion
Mentioned in topic(s): topic_Control
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [0/998] in all abinit tests, [0/117] in abinit tutorials

PAPI aims to provide the tool designer and application engineer with a consistent interface and methodology for use of the performance counter hardware found in most major microprocessors. PAPI enables software engineers to see, in near real time, the relation between software performance and processor events. This option can be used only when ABINIT has been compiled with the --enable-papi configure option. If papiopt = 1, then PAPI counters are used instead of the usual time() routine. All the timing output of ABINIT is then done with PAPI values. The measurements are more accurate and give also access to the flops of the calculation.

## pawprt_b¶

Mnemonics: PAW PRinT band
Characteristics: DEVELOP
Mentioned in topic(s): topic_PAW
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [0/998] in all abinit tests, [0/117] in abinit tutorials

Forces the output of the all-electron wavefunction for only a single band. To be used in conjuction with: pawprtwf = 1 and pawprt_k. The indexing of the bands start with one for the lowest occupied band and goes up from there.

## pawprt_k¶

Mnemonics: PAW PRinT K-point
Characteristics: DEVELOP
Mentioned in topic(s): topic_PAW
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [0/998] in all abinit tests, [0/117] in abinit tutorials

Forces the output of the all-electron wavefunction for only a single k-point. To be used in conjunction with: pawprtwf = 1 and pawprt_b. The indexing follows the order in ouptput of the internal variable kpt in the beginning of the run.

## pawujat¶

Mnemonics: PAW+macro_UJ, ATom number
Characteristics: DEVELOP
Mentioned in topic(s): topic_DFT+U
Variable type: integer
Dimensions: scalar
Default value: 1
Comment: i.e. the first atom treated with PAW+U.

Test list (click to open). Rarely used, [2/998] in all abinit tests, [1/117] in abinit tutorials

Determines the atom for which U (or J) should be determined. See also macro_uj.

Characteristics: DEVELOP
Mentioned in topic(s): topic_DFT+U
Variable type: real
Dimensions: scalar
Default value: 20 a.u.

Test list (click to open). Rarely used, [2/998] in all abinit tests, [1/117] in abinit tutorials

The sphere radius serves to extrapolate the U value calculated at r_paw to a larger sphere radius. See also macro_uj. As most projector functions are localized within r_paw to ≈80%, 20 a.u. contains ≈100% of the wavefunction and corresponds to r_paw -> ∞.

## pawujv¶

Mnemonics: PAW+macro_UJ, potential shift (V)
Characteristics: DEVELOP
Mentioned in topic(s): topic_DFT+U
Variable type: real
Dimensions: scalar
Default value: 0.1 eV

Test list (click to open). Rarely used, [2/998] in all abinit tests, [1/117] in abinit tutorials

Amplitude of the potential shift for the determination of U (or J). See also macro_uj.

## plowan_bandf¶

Mnemonics: Projected Local Orbital WANnier functions BAND Final
Characteristics: DEVELOP
Mentioned in topic(s): topic_Wannier
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [2/998] in all abinit tests, [0/117] in abinit tutorials

Gives the upper band to include in the calculation of Wannier functions

## plowan_bandi¶

Mnemonics: Projected Local Orbital WANnier functions BAND Initial
Characteristics: DEVELOP
Mentioned in topic(s): topic_Wannier
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [2/998] in all abinit tests, [0/117] in abinit tutorials

Gives the lower band to include in the calculation of Wannier functions

## plowan_compute¶

Mnemonics: Projected Local Orbital WANnier functions COMPUTATION
Characteristics: DEVELOP
Mentioned in topic(s): topic_Wannier
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [2/998] in all abinit tests, [0/117] in abinit tutorials

Activate computation of Projected Local Orbital Wannier functions (PLO Wannier) and corresponding band structure. Variables plowan_bandi, plowan_bandf, plowan_natom, plowan_nbl, plowan_iatom, plowan_lcalc, plowan_projcalc are mandatory to precise the nature of the projections.

• 0 → Default value: do not activate calculation of PLO Wannier.
• 1 → Compute PLO Wannier and band structure
• 2 → Compute PLO Wannier and band structure. In this case, the coupling in k-space between blocks of Wannier functions belonging to different angular momenta or atoms is removed.

Other related variables are plowan_realspace, plowan_nt, plowan_it. The implementation is not symetrized over k-point and not parallelized. (The calculation of projections is detailed in [Amadon2008] )

## plowan_iatom¶

Mnemonics: Projected Local Orbital WANnier functions, Index of ATOM
Characteristics: DEVELOP
Mentioned in topic(s): topic_Wannier
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [2/998] in all abinit tests, [0/117] in abinit tutorials

Gives the indices of the plowan_natom atoms on which the projections will be done.

## plowan_it¶

Mnemonics: Projected Local Orbital WANnier functions, Index of Translation.
Characteristics: DEVELOP
Mentioned in topic(s): topic_Wannier
Variable type: integer
Dimensions: (3,plowan_nt)
Default value: 0

Test list (click to open). Rarely used, [2/998] in all abinit tests, [0/117] in abinit tutorials

Requires plowan_realspace to be greater than 0 and plowan_nt to be greater than 0. Precise a given set of selected real space translation by using the real space vectors basis. These atoms are used to define Wannier functions in real space. These real space Wannier functions are used as a basis to compute the Hamiltonian.

## plowan_lcalc¶

Mnemonics: Projected Local Orbital WANnier functions, L values to use for CALCulation
Characteristics: DEVELOP
Mentioned in topic(s): topic_Wannier
Variable type: integer
Dimensions: (sum(plowan_nbl))
Default value: -1

Test list (click to open). Rarely used, [2/998] in all abinit tests, [0/117] in abinit tutorials

Gives the plowan_nbl values of angular momenta for each atom, in the order of the atoms as given in plowan_iatom.

## plowan_natom¶

Mnemonics: Projected Local Orbital WANnier functions, Number of ATOMs
Characteristics: DEVELOP
Mentioned in topic(s): topic_Wannier
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [2/998] in all abinit tests, [0/117] in abinit tutorials

Gives the number of atoms on which the projection will be done

## plowan_nbl¶

Mnemonics: Projected Local Orbital WANnier functions, NumBer of L values
Characteristics: DEVELOP
Mentioned in topic(s): topic_Wannier
Variable type: integer
Dimensions: (plowan_natom)
Default value: 0

Test list (click to open). Rarely used, [2/998] in all abinit tests, [0/117] in abinit tutorials

Gives the total number of angular momenta (over all atoms) to compute the projections.

## plowan_nt¶

Mnemonics: Projected Local Orbital WANnier functions, Number of Translation on which the real space values of energy are computed
Characteristics: DEVELOP
Mentioned in topic(s): topic_Wannier
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [2/998] in all abinit tests, [0/117] in abinit tutorials

Requires plowan_realspace to be greater than 0. Gives a number of selected atoms. These atoms are used to define Wannier functions in real space. These real space Wannier functions are used as a basis to compute the Hamiltonian.

## plowan_projcalc¶

Mnemonics: Projected Local Orbital WANnier functions, PROJectors values to use for CALCulation
Characteristics: DEVELOP
Mentioned in topic(s): topic_Wannier
Variable type: integer
Dimensions: (sum(plowan_nbl))
Default value: -1

Test list (click to open). Rarely used, [2/998] in all abinit tests, [0/117] in abinit tutorials

Gives the plowan_nbl values of projectors for each atom, in the order of the atoms as given in plowan_iatom. The index i for the projectors refers to the ith number on line orbitals of the PAW atomic data file.

## plowan_realspace¶

Mnemonics: Projected Local Orbital WANnier functions, activate REAL SPACE calculation.
Characteristics: DEVELOP
Mentioned in topic(s): topic_Wannier
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [2/998] in all abinit tests, [0/117] in abinit tutorials

Can take the following values:

• 0 → Default value: do not activate calculation of real space Wannier functions.
• 1 → Compute PLO Wannier in real space for analysis. These data can also be used in a following dataset to perform a Wannier interpolation.
• 2 → Do simple Wannier Interpolation for a given k points starting from real space Wannier function Hamiltonian computed in a preceding dataset.

## prepscphon¶

Mnemonics: PREPare Self-Consistent PHONon calculation
Characteristics: DEVELOP
Mentioned in topic(s): topic_printing
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [0/998] in all abinit tests, [0/117] in abinit tutorials

Print PCINFO, PHFREQ, and PHVEC files, for use with self-consistent phonon runs, after a perturbation calculation. Only prints out files for the present q-point, and there is presently no tool to symmetrize or merge these files, so use anaddb instead (with prtscphon input variable). The abinit input variable is destined to someday bypass the use of anaddb for scphon calculations.

## prtbltztrp¶

Mnemonics: PRinT output for BoLTZTRaP code
Characteristics: DEVELOP
Mentioned in topic(s): topic_printing
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [2/998] in all abinit tests, [0/117] in abinit tutorials

Print out geometry _BLZTRP_GEOM and eigenenergy _BLZTRP_EIGEN files for the BoltzTraP code by Georg Madsen.

## prtcif¶

Mnemonics: PRinT Crystallographic Information File
Characteristics: DEVELOP
Mentioned in topic(s): topic_printing
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [3/998] in all abinit tests, [1/117] in abinit tutorials

If set to 1, a CIF file is output with the crystallographic data for the present run (cell size shape and atomic positions).

## prtdipole¶

Mnemonics: PRinT DIPOLE
Characteristics: DEVELOP
Mentioned in topic(s): topic_printing
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

Print out dipole of unit cell, calculated in real space for the primitive cell only. Under development.

## prtnest¶

Mnemonics: PRinT NESTing function
Characteristics: DEVELOP
Mentioned in topic(s): topic_printing
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [4/998] in all abinit tests, [0/117] in abinit tutorials

If set to 1, the nesting function for the k-point grid is printed. For the moment the path in q space for the nesting function is fixed, but will become an input as well.

## prtposcar¶

Mnemonics: PRinT POSCAR file
Characteristics: DEVELOP
Mentioned in topic(s): topic_printing
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

Print out VASP-style POSCAR and FORCES files, for use with PHON or frophon codes for frozen phonon calculations. See the associated script in

interfacing with PHON, PHONOPY, etc…

## recefermi¶

Mnemonics: RECursion - initial guess of the FERMI Energy
Characteristics: DEVELOP
Mentioned in topic(s): topic_Recursion
Variable type: real
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [3/998] in all abinit tests, [0/117] in abinit tutorials

Used in Recursion method (tfkinfunc = 2). In the first SCF calculation it fixes the initial guess for the Fermi energy.

## recgratio¶

Mnemonics: RECursion - Grid RATIO
Characteristics: DEVELOP
Mentioned in topic(s): topic_Recursion
Variable type: integer
Dimensions: scalar
Default value: 1

Test list (click to open). Rarely used, [2/998] in all abinit tests, [0/117] in abinit tutorials

Used in Recursion method (tfkinfunc = 2). It represents the ratio of the two grid step: recgratio = fine_step/coarse_step and it is bigger or equal than 1. It introduces a double-grid system which permits to compute the electronic density on a coarse grid, using a fine grid (defined by ngfft) in the discretisation of the green kernel (see recptrott). Successively the density and the recursion coefficients are interpolated on the fine grid by FFT interpolation. Note that ngfft/recgratio=number of points of the coarse grid has to be compatible with the parallelization parameters.

## recnpath¶

Mnemonics: RECursion - Number of point for PATH integral calculations
Characteristics: DEVELOP
Mentioned in topic(s): topic_Recursion
Variable type: integer
Dimensions: scalar
Default value: 500

Test list (click to open). Rarely used, [3/998] in all abinit tests, [0/117] in abinit tutorials

Used in Recursion method (tfkinfunc = 2). Determine the number of discretisation points to compute some path integral in the recursion method; those path integrals are used to compute the entropy and the eigenvalues energy. during the latest SFC cycles.

## recnrec¶

Mnemonics: RECursion - Number of RECursions
Characteristics: DEVELOP
Mentioned in topic(s): topic_Recursion
Variable type: integer
Dimensions: scalar
Default value: 10

Test list (click to open). Rarely used, [3/998] in all abinit tests, [0/117] in abinit tutorials

Used in Recursion method (tfkinfunc = 2). Determine the maximum order of recursion, that is the dimension of the krylov space we use to compute density. If the precision set by rectolden is reached before that order, the recursion method automatically stops.

## recptrott¶

Mnemonics: RECursion - TROTTer parameter
Characteristics: DEVELOP
Mentioned in topic(s): topic_Recursion
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [3/998] in all abinit tests, [0/117] in abinit tutorials

Used in Recursion method (tfkinfunc = 2). Determine the trotter parameter used to compute the exponential of the hamiltonian in the recursion method:

e^{-\beta(-\Delta + V)} \approx \left( e^{-\frac{\beta}{4c} V} e^{-\frac{\beta}{4c} \Delta} e^{-\frac{\beta}{4c} V} \right)^{2c}

where $c$=recptrott. If set to 0, we use recptrott = $1/2$ in the above formula. Increasing recptrott improve the accuracy of the trotter formula, but increase the dicretisation error: it may be necessary to increase ngfft. The discretisation error is essentially the discretisation error of the green kernel $e^{\frac{c}{\beta|r|^2}}$ on the ngfft grid.

## recrcut¶

Characteristics: DEVELOP
Mentioned in topic(s): topic_Recursion
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [3/998] in all abinit tests, [0/117] in abinit tutorials

Used in Recursion method (tfkinfunc = 2). Used to improve the computational time in the case of the recursion method in a large cell: the density at a point will be computed with taking account only of a sphere of radius recrcut.

## rectesteg¶

Mnemonics: RECursion - TEST on Electron Gas
Characteristics: DEVELOP
Mentioned in topic(s): topic_Recursion
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

Used in Recursion method (tfkinfunc = 2). It is used to test an electron gas by putting the ion potential equal to zero.

## rectolden¶

Mnemonics: RECursion - TOLerance on the difference of electronic DENsity
Characteristics: DEVELOP
Mentioned in topic(s): topic_Recursion
Variable type: real
Dimensions: scalar
Default value: 0.0
Comment: Default value to be changed.

Test list (click to open). Rarely used, [3/998] in all abinit tests, [0/117] in abinit tutorials

Used in Recursion method (tfkinfunc = 2). Sets a tolerance for differences of electronic density that, reached TWICE successively, will cause one SCF cycle to stop. That electronic density difference is computed in the infinity norm (that is, it is computed point-by-point, and then the maximum difference is computed).

## symmorphi¶

Mnemonics: SYMMORPHIc symmetry operation selection
Characteristics: DEVELOP
Mentioned in topic(s): topic_crystal, topic_GW
Variable type: integer
Dimensions: scalar
Default value: 1

Test list (click to open). Moderately used, [29/998] in all abinit tests, [5/117] in abinit tutorials

With symmorphi = 1, symmetry operations with a non-symmorphic vector are allowed. With symmorphi = 0, they are not allowed. In the latter case, if the symmetry operations are specified in the input file, the code will stop and print an error message if a non-symmorphic vector is encountered. By contrast, if the symmetry operations are to be determined automatically (if nsym = 0), then the set of symmetries will not include the non-symmorphic operations.

Note: this feature exist because in a previous status of the GW calculations, non-symmorphic symmetry operations could not be exploited. Thus, the k points were restricted to the IBZ. In order to prepare GW calculations, and to perform GW calculations, symmorphi = 0 was to be used, together with nsym = 0.

## tfkinfunc¶

Mnemonics: Thomas-Fermi KINetic energy FUNCtional
Characteristics: DEVELOP
Mentioned in topic(s): topic_Recursion
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [7/998] in all abinit tests, [0/117] in abinit tutorials
• tfkinfunc = 1: Thomas-Fermi kinetic functional (explicit functional of the density) is used instead of Kohn-Sham kinetic energy functional (implicit functional of the density through Kohn-Sham wavefunctions). See [Perrot1979].

• tfkinfunc = 11: Thomas-Fermi-Weizsacker kinetic functional with Gradient Corrections is used. The convergence of a calculation with this functional needs to be initialized from a calculation without Gradient Correction. This is automatically done with tfkinfunc = 11. For the initialization steps, the tfw_toldfe criterion is used. When it is reached, then the Gradient Correction is added and the SCF cycle continues. Note: to obtain the convergence of a Molecular Dynamics simulation with TFW, it is necessary to find the best set of preconditionning parameters (diemix, diemac, dielng) and the best value of npulayit (if the default Pulay mixing is used).

• tfkinfunc = 12: same as tfkinfunc =11, but without the initialization steps. Gradient correction is directly added.

• tfkinfunc = 2: the Recursion Method is used in order to compute electronic density, entropy, Fermi energy and eigenvalues energy. This method computes the density without computing any orbital, is efficient at high temperature, with a efficient parallelization (almost perfect scalability). When that option is in use, the ecut input variable is no longer a convergence parameter; ngfft becomes the main convergence parameter: you should adapt ecut for the ngfft grid you need (it is not yet automatically computed). Other convergence parameter are for the energetic values: recnrec, recptrott, recnpath.

Since the convergence of the self-consistent cycle is determined directly by the convergence of the density: toldfe, toldff, tolrff, tolvrs, tolwfr are not used, and are replaced by rectolden; the energetic values, except for the fermi energy, are only computed during the latest SFC cycle: the output file will show a jump of the total energy at the end, but it is not because of a bad convergence behavior. Computational speed can be improved by the use of recrcut and recgratio. The recursion method has not been tested in the case of non cubic cell or with the use of symmetries. In the recursion method the following variables are set to: useylm = 1, %userec = 1.

## tfw_toldfe¶

Mnemonics: Thomas-Fermi-Weizsacker: TOLerance on the DiFference of total Energy, for initialization steps
Characteristics: ENERGY
Mentioned in topic(s): topic_Recursion
Variable type: real
Dimensions: scalar
Default value: 1.0E-6 or toldfe is present
Only relevant if: tfkinfunc = 11

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

This input variable has the same definition as toldfe and is only relevant when tfkinfunc = 11. It sets a tolerance for absolute differences of total energy that, reached TWICE successively, will cause the initialization steps (without gradient correction) to stop and the gradient correction to be added. Can be specified in Ha (the default), Ry, eV or Kelvin, since it has the ‘ENERGY’ characteristics.

## tolrde¶

Mnemonics: TOLerance on the Relative Difference of Eigenenergies
Mentioned in topic(s): topic_SCFControl
Variable type: real
Dimensions: scalar
Default value: 0.005

Test list (click to open). Moderately used, [11/998] in all abinit tests, [1/117] in abinit tutorials

Sets a tolerance for the ratio of differences of eigenenergies in the line minimisation conjugate-gradient algorithm. It compares the decrease of the eigenenergy due to the last line minimisation, with the one observed for the first line minimisation. When the ratio is lower than tolrde, the next line minimisations are skipped. The number of line minimisations is limited by nline anyhow. This stopping criterion is present for both GS and RF calculations. In RF calculations, tolrde is actually doubled before comparing with the above- mentioned ratio, for historical reasons.

## use_gemm_nonlop¶

Mnemonics: USE the GEMM routine for the application of the NON-Local OPerator
Characteristics: DEVELOP
Mentioned in topic(s): topic_parallelism
Variable type: integer
Dimensions: scalar
Default value: 0
Comment: because it is not usually worth using it unless bandpp is large and it requires additional memory

Test list (click to open). Rarely used, [3/998] in all abinit tests, [0/117] in abinit tutorials

This keyword tells abinit to use a BLAS routine to speed up the computation of the non-local operator. This requires the pre-computation of a large matrix, and has a significant memory overhead. In exchange, it provides improved performance when used on several bands at once (Chebyshev or LOBPCG algorithm with bandpp

The memory overhead is proportional to the number of atoms, the number of plane waves, and the number of projectors per atom. It can be mitigated by distributing the array with npfft

The performance depends crucially on having a good BLAS installed. Provided the BLAS supports OpenMP, this option also yields very good scaling for the nonlocal operator.

## use_nonscf_gkk¶

Mnemonics: USE NON-SCF calculation of GKK matrix elements (electron phonon)
Characteristics: DEVELOP
Mentioned in topic(s): topic_ElPhonInt
Variable type: integer
Dimensions: scalar
Default value: 0
Comment: Default is 0 for the moment. Do not use non-scf method.

Test list (click to open). Rarely used, [5/998] in all abinit tests, [1/117] in abinit tutorials

When this flag is activated during a phonon calculation with abinit, all of the perturbations are cycled through, but only the symmetry-irreducible ones are calculated self-consistently. For the others the perturbed density is rotated by the appropriate symop and the gkk matrix elements are calculated non-self-consistently. As they do not depend on the perturbed wave functions, they are correct from the first iteration, and nstep is set to 1 for those perturbations. Note that the resulting 1DEN files are simply the rotate/symmetric ones and that the resulting 1WF files are garbage (completely unconverged) except the matrix elements in the header (equivalent to GKK files, but please use the latter much smaller files for el-ph calculations). The new default behavior with use_nonscf_gkk = 1 should be transparent for the user, with the same output files but a much quicker execution.

Caveat: Note that very tight convergence of ground state and phonon calculations is necessary to get good GKK matrix elements! tolwfr = 1.e-24 or so is recommended everywhere. There may be problems using use_nonscf_gkk = 1 with non-symmorphic symmetries - please check (at least) that lifetimes for phonons go to 0 for acoustic modes at Gamma.

## usedmft¶

Mnemonics: USE Dynamical Mean Field Theory
Characteristics: DEVELOP
Mentioned in topic(s): topic_DMFT
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Moderately used, [24/998] in all abinit tests, [0/117] in abinit tutorials

If set to 1, enable the use of DFT+DMFT, see in particular the important variables dmft_solv, dmftbandi, dmftbandf, dmft_nwli, dmft_nwlo, dmft_tollc, dmft_tolfreq, and dmft_iter.

The current implementation uses Wannier functions obtained from projected local orbitals as correlated orbitals (see dmftbandi and dmftbandf input variables to define them).

The Green functions are computed on a mesh of linear Matsubara frequencies. However, most of the code uses logarithmic Matsubara grid to lower the computational cost. Both dmft_nwli and dmft_nwlo are thus convergence parameters.

DMFT is currently available for collinear (nspinor = 1) polarized or unpolarized calculations (nspden = nsppol = 2 or nspden = nsppol = 1) and for non collinear calculations (nspinor = 2,nspden = 4,nsppol = 1). However it is not yet available for collinear antiferromagnetic calculations (nspden = 2,nsppol = 1) and non collinear non magnetic calculations (nspden = 1, nsppol = 1,nspinor = 2). CTQMC calculations (dmft_solv = 5) are not yet possible if nspinor = 2.

Only static calculations without relaxation or dynamics are possible (forces and stress are not computed in the scheme: so the computed values should NOT be trusted).

When correlated density matrices are diagonal, all values of upawu and jpawu are possible. If the correlated density matrices are non diagonal, only jpawu = 0 is implemented.

Relevant direct output quantities from converged DMFT calculations are total energy and occupation of correlated orbitals. For Hubbard I calculation (dmft_solv = 2), total and partial spectral functions can be obtained with prtdos=1 and can be found in files OUTSpFunc* (where OUT is the root for output files). For CTQMC calculations (dmft_solv = 5), imaginary time impurity Green function are output of the calculations and can be used to produce spectral function using an external Maximum Entropy Code.

A typical DFT+DMFT calculation involves two runs. First, a DFT calculation is fully converged (even unoccupied wavefunctions have to be converged). Then, the DFT+DMFT calculation is started using DFT wavefunctions or density files. As DFT+DMFT calculations (with CTQMC) are computationally expensive, it is convenient to use prtden=-1, to write DEN file at each DFT iteration, in order to be able to restart the calculation easily.

For details of the implementation with Wannier functions see [Amadon2008], for self-consistency and Hubbard I implementation see [Amadon2012]. If usedmft = 1 and nbandkss/=0, then, the DFT+DMFT calculation is not done and only projections are computed at the end of the calculation. They can be used by an external code or used to compute the screened interaction (see variable ucrpa).

## usepotzero¶

Mnemonics: USE POTential ZERO
Mentioned in topic(s): topic_Coulomb
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

Fix the convention for the choice of the average value of the Hartree potential, as described in [Bruneval2014]. * usepotzero = 0, the usual convention: the smooth potential is set to zero average value. * usepotzero = 1, the new convention: the all-electron physical potential is set to zero average value. * usepotzero = 2, the PWscf convention: the potential of equivalent point charges is set to zero average value (convention also valid for NC pseudopotentials).

## useria¶

Mnemonics: USER Integer variable A
Mentioned in topic(s): topic_Dev
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [0/998] in all abinit tests, [0/117] in abinit tutorials

These are user-definable integers which the user may input and then utilize in subroutines of his/her own design. They are not used in the official versions of the ABINIT code, and should ease independent developments (hopefully integrated in the official version afterwards). Internally, they are available in the dtset structured datatype, e.g. dtset%useria.

## userib¶

Mnemonics: USER Integer variable B
Mentioned in topic(s): topic_Dev
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [0/998] in all abinit tests, [0/117] in abinit tutorials

These are user-definable integers which the user may input and then utilize in subroutines of his/her own design. They are not used in the official versions of the ABINIT code, and should ease independent developments (hopefully integrated in the official version afterwards). Internally, they are available in the dtset structured datatype, e.g. dtset%useria.

## useric¶

Mnemonics: USER Integer variable C
Mentioned in topic(s): topic_Dev
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [0/998] in all abinit tests, [0/117] in abinit tutorials

These are user-definable integers which the user may input and then utilize in subroutines of his/her own design. They are not used in the official versions of the ABINIT code, and should ease independent developments (hopefully integrated in the official version afterwards). Internally, they are available in the dtset structured datatype, e.g. dtset%useria.

## userid¶

Mnemonics: USER Integer variable D
Mentioned in topic(s): topic_Dev
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [0/998] in all abinit tests, [0/117] in abinit tutorials

These are user-definable integers which the user may input and then utilize in subroutines of his/her own design. They are not used in the official versions of the ABINIT code, and should ease independent developments (hopefully integrated in the official version afterwards). Internally, they are available in the dtset structured datatype, e.g. dtset%useria.

## userie¶

Mnemonics: USER Integer variable E
Mentioned in topic(s): topic_Dev
Variable type: integer
Dimensions: scalar
Default value: 0

Test list (click to open). Rarely used, [0/998] in all abinit tests, [0/117] in abinit tutorials

These are user-definable integers which the user may input and then utilize in subroutines of his/her own design. They are not used in the official versions of the ABINIT code, and should ease independent developments (hopefully integrated in the official version afterwards). Internally, they are available in the dtset structured datatype, e.g. dtset%useria.

## userra¶

Mnemonics: USER Real variable A
Mentioned in topic(s): topic_Dev
Variable type: real
Dimensions: scalar
Default value: 0.0

Test list (click to open). Rarely used, [0/998] in all abinit tests, [0/117] in abinit tutorials

These are user-definable with the same purpose as useria and cie.

## userrb¶

Mnemonics: USER Real variable B
Mentioned in topic(s): topic_Dev
Variable type: real
Dimensions: scalar
Default value: 0.0

Test list (click to open). Rarely used, [0/998] in all abinit tests, [0/117] in abinit tutorials

These are user-definable with the same purpose as useria and cie.

## userrc¶

Mnemonics: USER Real variable C
Mentioned in topic(s): topic_Dev
Variable type: real
Dimensions: scalar
Default value: 0.0

Test list (click to open). Rarely used, [0/998] in all abinit tests, [0/117] in abinit tutorials

These are user-definable with the same purpose as useria and cie.

## userrd¶

Mnemonics: USER Real variable D
Mentioned in topic(s): topic_Dev
Variable type: real
Dimensions: scalar
Default value: 0.0

Test list (click to open). Rarely used, [0/998] in all abinit tests, [0/117] in abinit tutorials

These are user-definable with the same purpose as useria and cie.

## userre¶

Mnemonics: USER Real variable E
Mentioned in topic(s): topic_Dev
Variable type: real
Dimensions: scalar
Default value: 0.0

Test list (click to open). Rarely used, [0/998] in all abinit tests, [0/117] in abinit tutorials

These are user-definable with the same purpose as useria and cie.

## useylm¶

Mnemonics: USE YLM (the spherical harmonics)
Characteristics: DEVELOP
Mentioned in topic(s): topic_TuningSpeed
Variable type: integer
Dimensions: scalar
Default value: 1 if tfkinfunc == 1, 1 if %usepaw == 1, 0 otherwise.

Test list (click to open). Rarely used, [7/998] in all abinit tests, [0/117] in abinit tutorials

When this flag is activated, the non-local operator is applied using an algorithm based on spherical harmonics. Non-local projectors are used with their usual form:

P_{lmn}(r) = Y_{lm}(r) p_{ln}(r)

When useylm = 0, the sum over $Y_{lm}$ can be reduced to a Legendre polynomial form.

## wfoptalg¶

Mnemonics: WaveFunction OPTimisation ALGorithm
Characteristics: DEVELOP
Mentioned in topic(s): topic_SCFAlgorithms
Variable type: integer
Dimensions: scalar
Default value: AUTO_FROM_PSP
Comment: 0 when %usepaw = 0 (norm-conserving pseudopotentials), 10 when %usepaw = 1 (PAW); 114 if paral_kgb = 1.

Test list (click to open). Moderately used, [16/998] in all abinit tests, [0/117] in abinit tutorials

Allows one to choose the algorithm for the optimisation of the wavefunctions. The different possibilities are:

• wfoptalg = 0: standard state-by-state conjugate gradient algorithm, with no possibility to parallelize over the states;

• wfoptalg = 2: minimisation of the residual with respect to different shifts, in order to cover the whole set of occupied bands, with possibility to parallelize over blocks of states (or bands). The number of states in a block is defined in nbdblock. THIS IS STILL IN DEVELOPMENT.

• wfoptalg = 3: minimisation of the residual with respect to a shift. Available only in the non-self-consistent case iscf = -2, in order to find eigenvalues and wavefunctions close to a prescribed value.

• wfoptalg = 4: (see also wfoptalg = 14), a parallel code based on the Locally Optimal Block Preconditioned Conjugate Gradient (LOBPCG) method of [Knyazev2001]. The implementation rests on the matlab program by Knyazev [Knyazev2007]. For more information see [Bottin2008]

• wfoptalg = 10: (for PAW) standard state-by-state conjugate gradient algorithm, with no possibility to parallelize over the states, but modified scheme described in [Kresse1996] (modified kinetic energy, modified preconditionning, minimal orthogonalization, …);

• wfoptalg = 14: the recommended for parallel code, the same as wfoptalg = 4 except that the preconditioning of the block vectors does not depend on the kinetic energy of each band, and the orthogonalization after the LOBPCG algorithm is no longer performed. The first modification increases the convergence and the second one the efficiency.

• wfoptalg = 114: A new version of wfoptalg = 14 which is more efficient for few blocks and can take advantage of OpenMP if abinit is compiled with a multithreaded linear algebra library. With more than 1 thread npfft shoud NOT be used for the time being.

• wfoptalg = 1: new algorithm based on Chebyshev filtering, designed for very large number of processors, in the regime where LOBPCG does not scale anymore. It is not able to use preconditionning and therefore might converge slower than other algorithms. By design, it will not converge the last bands: it is recommended to use slightly more bands than necessary. For usage with tolwfr, it is imperative to use nbdbuf. For more performance, try use_gemm_nonlop. For more information, see the performance guide and the [Levitt2015]. Status: experimental but usable. Questions and bug reports should be sent to antoine (dot) levitt (at) gmail.com.

## xc_denpos¶

Mnemonics: eXchange-Correlation - DENsity POSitivity value
Characteristics: DEVELOP
Mentioned in topic(s): topic_xc
Variable type: real
Dimensions: scalar
Default value: 1e-14

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

For the evaluation of the exchange-correlation functionals, the density cannot be negative, or even too small (e.g. the LDA exchange kernel behaves like the density at power -(⅔), and the density is used at the denominator of different factors in GGAs and metaGGAs. xc_denpos is the smallest value that the density can assume at the time of the evaluation of a XC functional, in ABINIT. When then computed density drops below xc_denpos before attacking the evaluation of the XC functional, then it will be (only for that purpose) replaced by xc_denpos. Note that the evaluation of the gradients or other quantities that are density-dependent is performed before this replacement.

It has been observed that the SCF cycle of the Tran-Blaha mGGA can be quite hard to make converge, for systems for which there is some vacuum. In this case, setting xc_denpos to 1.0e-7 … 1.0e-6 has been seen to allow good convergence. Of course, this will affect the numerical results somehow, and one should play a bit with this value to avoid incorrect calculations.

## xc_tb09_c¶

Mnemonics: Value of the c parameter in the eXchange-Correlation TB09 functional
Mentioned in topic(s): topic_xc
Variable type: real
Dimensions: scalar
Default value: 99.99

Test list (click to open). Rarely used, [1/998] in all abinit tests, [0/117] in abinit tutorials

The modified Becke-Johnson exchange-correlation functional by Tran and Blaha reads:

V_x(r) = c V_x^{BR}(r) + (3c - 2) \frac{1}{\pi} \sqrt{\frac{5}{12}} \sqrt{2 \frac{t(r)}{\rho(r)}}

where $\rho(r)$ is the electron density, $t(r)$ is the kinetic-energy density, and $V_x^{BR}(r)$ is the Becke-Roussel potential.

In this equation the parameter $c$ can be evaluated at each SCF step according to the following equation:

c = \alpha + \beta \left( \frac{1}{V_{cell}} \int_{V_{cell}} \frac{|\nabla \rho(r)|}{\rho(r)} d^3r \right)^{1/2}

The $c$ parameter is evaluated thanks to the previous equation when xc_tb09_c is equal to the “magic” default value 99.99. The $c$ parameter can also be fixed to some (property-optimized or material-optimized) value by using this variable.