"The empirical pseudopotential method never lost a battle to experiment." -- Marvin L. Cohen, 2008
EPM stands for Empirical Pseudopotential Method. It is the plane-wave part of TBPW-1.1 modified to generate input files for BerkeleyGW. Numerous other corrections and improvements have also been made by Georgy Samsonidze and David Strubbe. TBPW-1.1 is available for download from http://www.mcc.uiuc.edu/software/, and the full documentation at: http://www.mcc.uiuc.edu/downloads/tbpwdoc1.1.pdf.
The input variables are described in
epm.inp. Most variables are common to both
epm2bgw.x, but a few are just for one or the other.
The real wavefunctions for systems with inversion symmetry
are obtained by applying the Gram-Schmidt process adapted from
To plot silicon band structure calculated with the EPM executable:
epm.x < silicon-epm.in gnuplot bands.plt
To use the explicit form factors and to compute the band gap and the effective masses (mass only correct for Si-like band structures):
epm.x < silicon-epm-ff.in
To generate input files for BerkeleyGW executable, use
epm2bgw_cplx_spin.sh are just for use
with the testsuite. They force complex, or complex and spin-polarized.
You can find the actual input files for GW/BSE calculations on top of
EPM in directory
examples/EPM, as well as testsuite directories
The k-points for the EPM input files can be generated using utility
Virtual crystal approximation (
VCA) is implemented within EPM in
the form of two pre-processing scripts,
ff2vq.py reads EPM form factors from file
form_factors.dat, fits them
to the chosen functional form of the V(q) potential, writes potential
coefficients to file
v_of_q.dat, and writes new form factors computed
from V(q) to file
vq2ff.dat. This procedure is described by equations
(8) and (9) and the accompanying text in Phys. Rev. B 84, 195201 (2011).
vca.py reads V(q) potential coefficients from file
employs the virtual crystal approximation to compute hybrid form
factors, and writes them to file
vca_ff.dat. The potential mixing
is controlled by identifiers host_material and doping_level hard
coded below. This procedure is described by equations (10) -- (12)
and the accompanying text in Phys. Rev. B 84, 195201 (2011).
The original form factors from file
form_factors.dat or the hybrid
ones from file
vca_ff.dat can be fed to
FormFactors in the input file for
epm2bgw.x. See example of using these keywords in
The original code that EPM was based on, TBPW-1.1, was written by:
- Dyutiman Das, UIUC
- William Mattson, UIUC
- Nichols A. Romero, UIUC
- Richard M. Martin, UIUC
Description of TBPW-1.1 Software
The full documentation of the TBPW code is available at http://www.mcc.uiuc.edu/downloads/tbpwdoc1.1.pdf.
TBPW is an electronic structure code primarily intended for pedagogical purposes. It is written from the ground-up in a modular style using Fortran 90. This code is composed of two distinct parts: a tightbinding (TB) and plane wave (PW). Additionally, there is a plane wave density (PWD) code which outputs the electron density on a grid.
The main characteristics of these codes are:
- Readily provides band structure plots
- TB implemented using a rotation matrix formalism allows the use of orbitals with arbitrary angular momentum l
- PW implemented using the option of diagonalisation via direct-inversion
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This material is based upon work supported by the NSF under Award No. 99-76550 and the DOE under Award No. DEFG-96-ER45439.
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