The fold2Bloch utility is designed to unfold the band structure of a supercell obtained with the Vienna Ab initio Simulation Package (VASP) and compute an effective band structure in a primitive representation. It facilitates interpretation of large-scale electronic structure calculations, where the Bloch character of electronic eigenstates is perturbed by a disorder (defects, alloy elements, etc). Reading of wavefunctions is adapted from the WaveTrans code.
- Oleg Rubel (McMaster University oleg.v.rubel@gmail.com)
- Michael Widom and Randall Feenstra (Carnegie Mellon University)
- Anton Bokhanchuk (Confederation College)
First clone the GitHub repository
$ git clone https://github.com/rubel75/fold2Bloch-VASP
The makefile is set up for Intel Fortran compiler ifort. To compile, simply execute
$ cd fold2Bloch-VASP; make
First, you need to perform the band structure calculation and generate WAVECAR file for the k-mesh of interest using standard VASP procedure (see VASP guidelines). (The folliwing Matlab script utils/fold.m is designed to assist with preparing a folded string of k-points that will unfold on a desired k-path.) It is advised to increase the number of empty bands (NBANDS=... in INCAR file) by a factor of 1.2-2 beyond a VASP-proposed defaul value to get a resonable description of higher energy states.
Once WAVECAR is ready, execute
/path/to/fold2Bloch WAVECAR FX:FY:FZ [-ncl]
Options:
WAVECAR -- name of the input VASP wavefunction file
FX:FY:FZ -- multiplicity of the primitive cell that was used to construct a supercell. Note: the supercell should be constracted on the basis of the primitive cell (not conventional).
-ncl -- optional switch that needs to be activated when the WAVECAR is produced by vasp_ncl code, which implies that the wavefunctions are spinors (default assumption is that WAVECAR comes from vasp_std or vasp_gam).
Output is writen to WAVECAR_*.f2b file(s). There is one output file for non-spin-polarized calculation and two files for the spin-polarized or spinor (vasp_ncl) calculations. Below is a sample of an output file.
New K-values (x, y, z) Eigenvalue (eV) Weight
0.000000 0.000000 0.000000 -22.019998 1.000000
0.000000 0.200000 0.000000 -22.019998 0.000000
0.000000 0.400000 0.000000 -22.019998 0.000000
0.000000 -0.400000 0.000000 -22.019998 0.000000
0.000000 -0.200000 0.000000 -22.019998 0.000000
0.200000 0.000000 0.000000 -22.019998 0.000000
...
The Matlab code utils/ubs_dots_VASP.m is designed to assist with plotting the band structure and the Bloch weights. Please refer to its input section for description of user input variables. Below is a sample of the Matlab plot for the unfolded band structure of a dilute GaP:N alloy.
If you find the results usefull and publishable, we will appreciate citing the following papers:
- O. Rubel, A. Bokhanchuk, S. J. Ahmed, and E. Assmann "Unfolding the band structure of disordered solids: from bound states to high-mobility Kane fermions", Phys. Rev. B 90, 115202 (2014).
- V. Popescu and A. Zunger "Effective Band Structure of Random Alloys", Phys. Rev. Lett. 104, 236403 (2010).
fold2Bloch is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
fold2Bloch is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.