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"The empirical pseudopotential method never lost a battle to experiment."
-- Marvin Cohen, 2008

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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/

The input variables are described in epm.inp. Most variables are common to both
epm.x and 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 
paratecSGL-1.1.3/src/para/gwreal.f90

To plot silicon band structure calculated with the EPM executable:
% epm.x < silicon-epm.in
% gnuplot bands.plt
Uses variables NumberOfLines, NumberOfDivisions, KPointsAndLabels.

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
Uses variables gap_flag, gap_file, mass_flag, mass_file.

To generate input files for BerkeleyGW executable, use epm2bgw.x.
The scripts epm2bgw_cplx.sh and 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
Si-EPM, GaAs-EPM, and Si-Wire-EPM.

The k-points for the EPM input files can be generated using utility 
kgrid. Please refer to file MeanField/ESPRESSO/README for details.

Virtual crystal approximation (VCA) is implemented within EPM in 
the form of two pre-processing scripts, ff2vq.py and vca.py.

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 v_of_q.dat, 
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 epm.x and epm2bgw.x using 
keywords LatticeConstant and FormFactors in the input file for epm.x 
or epm2bgw.x. See example of using these keywords in silicon-epm-ff.in.

The README file of TBPW-1.1 follows below.

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TBPW-1.1

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Author/Affiliation

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 * Dyutiman Das, UIUC
 * William Mattson, UIUC
 * Nichols A. Romero, UIUC
 * Richard M. Martin, UIUC

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Author email

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nromero@uiuc.edu

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Description of Software

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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

Send email to tbpw-subscribe@mcc.uiuc.edu to subscribe to the mailing list, tbpw@mcc.uiuc.edu

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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Submitted

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2003-01-31

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Disclaimer

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Developed by Electronic Structure Group, University of Illinois, Department of Physics, http://www.physics.uiuc.edu/research/ElectronicStructure/ Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the Software), to deal with the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

 * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimers.
 * Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimers in the documentation and/or other materials provided with the distribution.
 * Neither the names of the Electronic Structure Group, the University of Illinois, nor the names of its contributors may be used to endorse or promote products derived from this Software without specific prior written permission.

THE SOFTWARE IS PROVIDED AS IS, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE CONTRIBUTORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS WITH THE SOFTWARE.

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Copyright

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University of Illinois Open Source License. Copyright (c) 2003, University of Illinois Board of Trustees. All rights reserved. Users also agree to terms of License Agreement available at http://www.mcc.uiuc.edu/

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