# eph input variables¶

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

**asr**¶

*Mnemonics:* Acoustic Sum Rule

*Mentioned in topic(s):* topic_DFPT

*Variable type:* integer

*Dimensions:* scalar

*Default value:* 1

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

Govern the imposition of the Acoustic Sum Rule (ASR) in phonon calculations. Same meaning as the corresponding anaddb variable.

**chneut**¶

*Mnemonics:* CHarge NEUTrality treatment

*Mentioned in topic(s):* topic_Phonons

*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

- v7: t88.in

Set the treatment of the Charge Neutrality requirement for the effective charges. Same meaning as the corresponding anaddb variable.

**ddb_ngqpt**¶

*Mnemonics:* Derivative DataBase: Number of Grid points for Q-PoinTs

*Mentioned in topic(s):* topic_ElPhonInt

*Variable type:* integer

*Dimensions:* (3)

*Default value:* [0, 0, 0]

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

This variable is mandatory when optdriver == 7. It defines the number of divisions in the (homogeneous) q-mesh used to generate the DDB file. See also the description of the getddb input variable.

**ddb_shiftq**¶

*Mnemonics:* Derivative DataBase: SHIFT of the Q-points

*Mentioned in topic(s):* topic_ElPhonInt

*Variable type:* real

*Dimensions:* (3)

*Default value:* [0.0, 0.0, 0.0]

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

Only relevant when optdriver == 7. It defines the shift in the q-mesh used to generate the DDB file, which is defined by the ddb_ngqpt input variable. See shiftk for more information on the definition.

**dipdip**¶

*Mnemonics:* DIPole-DIPole interaction

*Mentioned in topic(s):* topic_Phonons

*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

- v7: t88.in

This variable defines the treatment of the dipole-dipole interaction. Same meaning as the corresponding anaddb variable dipdip@anaddb

**eph_extrael**¶

*Mnemonics:* Electron-PHonon: EXTRA ELectrons

*Mentioned in topic(s):* topic_ElPhonInt

*Variable type:* real

*Dimensions:* scalar

*Default value:* 0.0

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

- v7: t88.in

Number of electrons per unit cell to be added to the initial value computed from the pseudopotentials and unit cell.

**eph_fermie**¶

*Mnemonics:* Electron-PHonon: FERMI Energy

*Characteristics:* ENERGY

*Mentioned in topic(s):* topic_ElPhonInt

*Variable type:* real

*Dimensions:* scalar

*Default value:* 0.0

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

- v7: t88.in

This variable can be used to change the value of the Fermi level when performing electron-phonon calculations with optdriver == 7. This variable has effect only if set to a non-zero value. See also eph_extrael.

**eph_frohlichm**¶

*Mnemonics:* Electron-PHonon: FROHLICH Model

*Mentioned in topic(s):* topic_ElPhonInt

*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

- v8: t57.in

Only relevant for optdriver=7 and eph_task=6. If set to 1, use the dynamical matrix at Gamma, the Born effective charges, the dielectric tensor, as well as the effective masses (must give a _EFMAS file as input, see prtefmas and getefmas or irdefmas), as the parameters of a Frohlich Hamiltonian. Then use these to compute the change of electronic eigenvalues due to electron-phonon interaction, using second-order time-dependent perturbation theory. Can deliver (approximate) zero-point renormalisation as well as temperature dependence.

**eph_fsewin**¶

*Mnemonics:* Electron-Phonon: Fermi Surface Energy WINdow

*Characteristics:* ENERGY

*Mentioned in topic(s):* topic_ElPhonInt

*Variable type:* real

*Dimensions:* scalar

*Default value:* 0.01 Hartree

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

- v7: t88.in

This variable defines the energy window around the Fermi level used for e-ph calculations (optdriver = 7). Only the states located in the energy range [efermi - eph_fsewin, efermi + eph_fsewin] are included in the e-ph calculation.

Related input variables: eph_intmeth, eph_fsmear, eph_extrael and eph_fermie.

**eph_fsmear**¶

*Mnemonics:* Electron-PHonon: Fermi surface SMEARing

*Characteristics:* ENERGY

*Mentioned in topic(s):* topic_ElPhonInt

*Variable type:* real

*Dimensions:* scalar

*Default value:* 0.01 Hartree

*Only relevant if:* eph_intmeth == 1

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

- v7: t88.in

This variable defines the gaussian broadening used for the integration over the Fermi surface when eph_intmeth == 1.

**eph_intmeth**¶

*Mnemonics:* Electron-Phonon: INTegration METHod

*Mentioned in topic(s):* topic_ElPhonInt

*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

- v7: t88.in

This variable defines the technique for the integration on the Fermi surface of electron-phonon quantities.

- 1 → Gaussian technique with broadening factor eph_fsmear.
- 2 → Tetrahedron method.

See also eph_fsewin, eph_extrael and eph_fermie.

**eph_mustar**¶

*Mnemonics:* Electron-PHonon: MU STAR (electron-electron interaction strength)

*Mentioned in topic(s):* topic_ElPhonInt

*Variable type:* real

*Dimensions:* scalar

*Default value:* 0.1

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

- v7: t88.in

Average electron-electron interaction strength, for the computation of the superconducting Tc using Mc-Millan’s formula.

**eph_ngqpt_fine**¶

*Mnemonics:* Electron-PHonon: Number of Grid Q-PoinTs in FINE grid.

*Mentioned in topic(s):* topic_ElPhonInt

*Variable type:* integer

*Dimensions:* (3)

*Default value:* [0, 0, 0]

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

This variable activates the **interpolation** of the first-order variation of the
self-consistent potential in the electron-phonon code (optdriver == 7).

If eph_nqgpt_fine differs from [0, 0, 0], the code will use the Fourier transform to interpolate
the DFPT potentials on this fine q-mesh starting from the irreducible set of
q-points read from the DVDB file. This approach is similar to the one used to
interpolate the interatomic force constants in q-space. If **eph_ngqpt_fine** is
not given, the EPH code uses the list of irreducible q-points reported in the
DDB file i.e. ddb_ngqpt (default behavior).

Important

The computation of the electron-phonon matrix elements requires the knowledge of \psi_{\bf k}
and \psi_{\bf k + q}. This means that the k-mesh for electrons found in the WFK must be
compatible with the one given in *eph_ngqpt_fine*.
The code can interpolate DFPT potentials but won’t try to interpolate KS wavefunctions.
and will stop if {\bf k + q} is not found in the WFK file.

**eph_task**¶

*Mnemonics:* Electron-PHonon: Task

*Mentioned in topic(s):* topic_ElPhonInt

*Variable type:* integer

*Dimensions:* scalar

*Default value:* 1

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

When optdriver == 7, select the task to be performed. The choice is among:

- 0 → No computation (mainly used to access the post-processing tools)
- 1 → Compute phonon linewidths in metals.
- 2 → Compute electron-phonon matrix elements.
- 3 → Compute phonon self-energy.
- 4 → Compute EPH self-energy (Fan-Migdal + Debye-Waller).
- 5 → Interpolate DFPT potentials.

**eph_transport**¶

*Mnemonics:* Electron-PHonon: TRANSPORT flag

*Mentioned in topic(s):* topic_ElPhonInt

*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

- v7: t88.in

NB - this does not work yet. This variable can be used to turn on the calculation of transport quantities in the eph module of abinit. Value of 1 corresponds to elastic LOVA as in the PRB by [Savrasov1996].

**ph_intmeth**¶

*Mnemonics:* PHonons: INTegration METHod

*Mentioned in topic(s):* topic_q-points

*Variable type:* integer

*Dimensions:* scalar

*Default value:* 2

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

Select the integration technique for computing the phonon DOS and the Eliashberg function \alpha^2F(\omega).

- 1 → Gaussian scheme (see also ph_smear).
- 2 → tetrahedron method (no other input is needed but requires at least 4 q-points in the BZ)

**ph_ndivsm**¶

*Mnemonics:* PHonons: Number of DIVisions for sampling the SMallest segment

*Mentioned in topic(s):* topic_q-points

*Variable type:* integer

*Dimensions:* scalar

*Default value:* 20

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

This variable is used in conjunction with ph_nqpath and ph_qpath to define the q-path used for phonon band structures and phonon linewidths. It gives the number of points used to sample the smallest segment in the q-path specified by ph_qpath.

**ph_ngqpt**¶

*Mnemonics:* PHonons: Number of Grid points for Q-PoinT mesh.

*Mentioned in topic(s):* topic_q-points

*Variable type:* integer

*Dimensions:* (3)

*Default value:* [20, 20, 20]

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

This variable defines the q-mesh used to compute the phonon DOS and the Eliashberg function via Fourier interpolation. Related input variables: ph_qshift and ph_nqshift.

**ph_nqpath**¶

*Mnemonics:* PHonons: Number of Q-points defining the PATH

*Mentioned in topic(s):* topic_q-points

*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

This integer defines the number of points in the ph_qpath array.

**ph_nqshift**¶

*Mnemonics:* PHonons: Number of Q-SHIFTs

*Mentioned in topic(s):* topic_q-points

*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

This variable defines the number of shifts in the q-mesh used for the phonon DOS and for the Eliashberg functions (see ph_ngqpt). If not given, the code assumes a Gamma-centered mesh. The shifts are specified by ph_qshift.

**ph_qpath**¶

*Mnemonics:* Phonons: Q-PATH

*Mentioned in topic(s):* topic_q-points

*Variable type:* real

*Dimensions:* (3,ph_nqpath)

*Default value:* None

*Only relevant if:* specified(ph_nqpath)

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

This array contains the list of special q-points used to construct the q-path used to (Fourier) interpolate phonon band structures and phonon linewidths. See also ph_nqpath and ph_ndivsm.

**ph_qshift**¶

*Mnemonics:* PHonons: Q-SHIFTs for mesh.

*Mentioned in topic(s):* topic_q-points

*Variable type:* real

*Dimensions:* (3,ph_nqshift)

*Default value:* [0, 0, 0]

*Only relevant if:* ph_nqshift

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

This array gives the shifts to be used to construct the q-mesh for computing the phonon DOS and the Eliashberg functions (see also ph_nqshift). If not given, a Gamma-centered mesh is used.

**ph_smear**¶

*Mnemonics:* PHonons: SMEARing factor

*Characteristics:* ENERGY

*Mentioned in topic(s):* topic_q-points

*Variable type:* real

*Dimensions:* scalar

*Default value:* 0.00002 Hartree

*Only relevant if:* ph_intmeth == 1

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

The gaussian broadening used for the integration of the phonon DOS and the Eliashberg function. See also ph_intmeth and ph_ngqpt.

**ph_wstep**¶

*Mnemonics:* PHonons: frequency(W) STEP.

*Characteristics:* ENERGY

*Mentioned in topic(s):* topic_q-points

*Variable type:* real

*Dimensions:* scalar

*Default value:* 0.1 meV

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

The step used to generate the (linear) frequency mesh for the phonon DOS and the Eliashberg function. The extrema of the mesh are automatically computed by the code.

**prtphbands**¶

*Mnemonics:* PRinT PHonon BANDS

*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

- v7: t88.in

This option activates the output of the phonon frequencies in the EPH code. Possible values:

- 0 Disable the output of the phonon frequencies.
- 1 Write frequencies in xmgrace format. A file with extension
`PHBANDS.agr`

is produced. Use`xmgrace file_PHBANDS.agr`

to visualize the data - 2 Write frequencies in gnuplot format. The code produces a
`PHBANDS.dat`

file with the eigenvalues and a`PHBANDS.gnuplot`

script. Use`gnuplot file_PHBANDS.gnuplot`

to visualize the phonon band structure.

**prtphdos**¶

*Mnemonics:* PRinT the PHonon Density Of States

*Characteristics:* DEVELOP

*Mentioned in topic(s):* topic_printing, topic_ElPhonInt

*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

Print the phonon density of states. It is activated by default when optdriver == 7.

**prtphsurf**¶

*Mnemonics:* PRinT PHonon iso-SURFace

*Mentioned in topic(s):* topic_printing, topic_ElPhonInt

*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

- v7: t88.in

Print a bxsf file (Xcrysden format) with the (interpolated) phonon frequencies computed of the q-mesh determined by ph_ngqpt. The file can be use to visualize isosurfaces with Xcrysden or other similar tools supporting the bxsf format. Note that the (dense) q-mesh must be Gamma-centered, shifted meshes are not supported by Xcrysden. This variable requires optdriver == 7.

**symdynmat**¶

*Mnemonics:* SYMmetrize the DYNamical MATrix

*Mentioned in topic(s):* topic_Phonons

*Variable type:* integer

*Dimensions:* scalar

*Default value:* 1

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

If symdynmat is equal to 1, the dynamical matrix is symmetrized before the diagonalization (same meaning as the corresponding anaddb variable). Note that symdynmat == 1 will automatically enable the symmetrization of the electron- phonon linewidths.

**tmesh**¶

*Mnemonics:* Temperature MESH

*Mentioned in topic(s):* topic_ElPhonInt

*Variable type:* real

*Dimensions:* (3)

*Default value:* [5.0, 59.0, 6.0]

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

This variable defines the linear mesh of temperatures used in the EPH code (optdriver = 7). The first entry gives the initial temperature in Kelvin, the second entry the linear step in Kelvin, the third entry is the number of points in the mesh. The default value corresponds to 6 points between 5 K and 300 K.