KG4VASP

version: v1.0 stable (stand alone)

Acknowledgements:

I would like to thank:

• kgec developers ¹ for their inspiring work and effort to deliver a nice tool for QE
• for the mathematical derivation of various quantities from the generalised Kubo-Greenwood formula ²
• Quantum espresso ³
• VASP ⁴

The code

This code is meant to be as a VASP post-processing tool for people that want to calculate transport properties.

The quantities calculated at the moment are:

1. Electrical conductivity/resistivity

2. Seebeck coefficient

3. Electron thermal conductivity

4. Possibly, a flavour of the relaxation time $\tau$ can be obtained by fitting $\sigma (\omega) = \sigma_0 / 1+\omega^2 \tau^2$ at $\omega \rightarrow 0$ (Drude Model)

   The INPUT file

   kg4vasp input file is called INPUT and needs that the following FLAGS have to be addressed:

   • SYSTEM (character): usually name of the system in study
   • NBANDS (integer): number of bands
   • FILE_NABLA (character): name of file where the DFT code stores nabla matrix elements
   • NKPOINTS (integer): number of K-POINTS
   • NP_FREQ (integer): number of frequency between min and max
   • DELTAE (real): energy threshold for degeneracy between two contiguous energies
   • MAX_FREQ (real): max value for frequency in eV
   • MIN_FREQ (real): min value for frequency in eV
   • GAUS_SIGMA (real): spreading in eV for delta function that is approximated by 1 gaussian function
   • VOLUME (real): cell volume in $Ang ^3$
   • DEGAUSS (real): electronic temperature $K_b \cdot T$ (degauss in quantum espresso and sigma in VASP if the smearing has been set up on ) in eV
   • INTRA_BAND (boolean): TRUE=in the calculation intraband and degerate energies are included; FALSE=other way round
   • FERMI_ENERGY (real): fermi energy from SCF (STATIC DFT CALCULATION) in eV
   • FROM_VASP (boolean): TRUE=post-processing of VASP calculations; FALSE=post-processing of QE calculations
   • OCC_FROM_CODE (boolean):
   • N_ELECTRON (integer): total number of electrons in the system
   • NABLA_BIN (boolean, default=.FALSE.): TRUE: the nabla file is in binary format; FALSE the nabla file is in ASCII formatted file.

The repository

The structure is the following:

1. src: source code in fortran90
   • check Makefile to update the fortran compiler: a) compile with make or 2) clean with make clean
2. examples: test drive for kg4vasp a) Simple VASP calculations b) from kgec code simple QE/kgec calculations c) comparison between them and validation
3. PATCHES: necessary for kgec v2.1 and VASP 5.4.4 to run kg4vasp on VASP matrix elements and on kgec/QE output as well.

Reference

1. L.Calderín, V.V.Karasiev2, S.B.Trickey, Computer Physics Communications Volume 221, December 2017, Pages 118-142

2. S.Mazevet,M.Torrent,V.Recoules,F.Jollet, High Energy Density Physics Volume 6, Issue 1, January 2010, Pages 84-88

3. Giannozzi, S. Baroni, et al J.Phys.:Condens.Matter 21, 395502 (2009)

4. G. Kresse and J. Hafner, Phys. Rev. B 47 , 558 (1993); ibid. 49 , 14 251 (1994)