This page gives hints on how to perform thermodynamic, elastic and transport properties calculations including explicit temperature effects with the ABINIT package.
The Temperature Dependent Effective Potential (TDEP) method has been developped by O. Hellman et al. [Hellman2011], [Hellman2013], [Hellman2013a] in 2011 and the |a-TDEP| implementation in ABINIT has been performed and used for the first time in 2015 by J. Bouchet and F. Bottin [Bouchet2015], [Bouchet2017].
The capture of thermal effects in solid state physic is a long standing issue and several stand-alone or post-process computational codes are available. Using different theoretical frameworks, they propose to provide some thermodynamic quantities involving the so called anharmonic effects. |a-TDEP| calculation can produce almost all the temperature-dependent thermodynamic quantities you want, from a single ab initio molecular dynamic (AIMD) trajectory and by means of a Graphical User Interface (GUI) very easy to use (AGATE).
The original TDEP method [Hellman2011] is implemented in ABINIT.
In particular, various algorithms can be used to obtain the Interatomic Force Constants (IFC).
The 2nd-order (and soon 3rd-order) IFCs are produced self-consistently using a least-square
method fitting the AIMD forces on a model Hamiltonian function of the displacements.
Numerous thermodynamic quantities can be computed starting from the 2nd order IFCs. The 1st one is the phonon spectra, from which a large number of other quantities flow : internal energy, entropy, free energy, specific heat… The elastic constants and other usual elastic moduli (the bulk, shear and Young moduli) can be also produced at this level. Using the 3rd order IFCs, we could extract the Gruneisen parameter, the thermal expansion, the sound velocities… and in particular, how to take into account the anisotropy of the system within.
Related Input Variables¶
- amu Atomic masses in Mass Units
- angle ANGLE alpha
- brav BRAVais
- multiplicity MULTIPLICITY
- natom NATOM
- natom_unitcell NATOM in the UNITCELL
- nstep_max NSTEP at MAX
- nstep_min NSTEP at MIN
- ntypat NTYPAT
- rcut Radius CUToff
- rprimd RPRIMD
- temperature TEMPERATURE
- typat TYPAT
- typat_unitcell TYPAT in the UNITCELL
- xred_unitcell XRED in the UNITCELL
- bzpath Brillouin Zone PATH
- dosdeltae DOS delta Energy
- enunit ENergy UNIT
- ngqpt1 Number of Grid points for Q PoinTs generation (coarse)
- ngqpt2 Number of Grid points for Q PoinTs generation (fine)
- order ORDER for the IFC
- slice SLICE
- use_ideal_positions USE IDEAL POSITIONS
Selected Input Files¶