Bandstructure of SrVO3 in GW: Difference between revisions
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from the {{FILE|INCAR}} file, and redo the GW step. | from the {{FILE|INCAR}} file, and redo the GW step. | ||
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Revision as of 15:35, 12 September 2012
Description: the GW bandstructure of SrVO3 using VASP and WANNIER90.
Performing a GW calculation with VASP is a 3-step procedure: a DFT groundstate calculation, a calculation to obtain a number of virtual orbitals, and the actual GW calculation itself. In this example we will also see how the results of the GW calculation may be postprocessed with WANNIER90 to obtain the dispersion of the bands along the usual high symmetry directions in reciprocal space.
The DFT groundstate calculation
Everthing starts with a conventional DFT (in this LDA) groundstate calculation:
- INCAR.DFT
System = SrVO3 NBANDS = 36 ISMEAR = -5 EMIN = -20 ; EMAX = 20 ; NEDOS = 1000 # usefull energy range for density of states EDIFF = 1E-8 # high precision for groundstate calculation KPAR = 3
Copy the aforementioned file to INCAR:
cp INCAR.DFT INCAR
- KPOINTS
Automatically generated mesh
0
Gamma
4 4 4
Mind: this is definitely not dense enough for a high-quality description of SrVO3, but in the interest of speed we will live with it.
- POSCAR
SrVO3 3.77706 #taken from 9x9x9 with sigma=0.2 ismear=2 +1.0000000000 +0.0000000000 +0.0000000000 +0.0000000000 +1.0000000000 +0.0000000000 +0.0000000000 +0.0000000000 +1.0000000000 Sr V O 1 1 3 Direct +0.0000000000 +0.0000000000 +0.0000000000 +0.5000000000 +0.5000000000 +0.5000000000 +0.5000000000 +0.5000000000 +0.0000000000 +0.5000000000 +0.0000000000 +0.5000000000 +0.0000000000 +0.5000000000 +0.5000000000
Analysis of the DOS
Add the following line to your INCAR file:
LORBIT = 11
and rerun VASP.
In addition to the total density-of-states (DOS), the DOSCAR now contains blocks of information with the site-projected lm-decomposed DOS as well, and the site-projected lm-decomposed band character is written to the PROCAR file.
To plot the total DOS and the Vanadium t2g and eg partial-DOS using gnuplot, execute the following command:
./plotdos
Mind: Check the OUTCAR file for the position of the Fermi level. These DOSs have not been shifted such that the Fermi level is at 0 eV.
Bandstructure using WANNIER90
Add the following line to your INCAR to have VASP call WANNIER90:
LWANNIER90_RUN = .TRUE.
WANNIER90 takes its input from the file wannier90.win. To construct Wannier functions for the Vanadium t2g manifold in SrVO3, and plot the dispersion of the associated bands along R-G-X-M, one may use the following settings:
- wannier90.win.dft
bands_plot = true begin kpoint_path R 0.50000000 0.50000000 0.50000000 G 0.00000000 0.00000000 0.00000000 G 0.00000000 0.00000000 0.00000000 X 0.50000000 0.00000000 0.00000000 X 0.50000000 0.00000000 0.00000000 M 0.50000000 0.50000000 0.00000000 M 0.50000000 0.50000000 0.00000000 G 0.00000000 0.00000000 0.00000000 end kpoint_path num_wann = 3 num_bands= 3 exclude_bands : 1-20, 24-36 begin projections V:dxy;dxz;dyz end projections
Copy the above to wannier90.win:
cp wannier90.win.dft wannier90.win
and restart VASP.
The Vanadium t2g band dispersion thus obtained, may conveniently be visualized with gnuplot:
gnuplot -persist plotme.dft
Mind: Here the eigenvalues have been shifted such that the Fermi level is a 0 eV.
Obtain DFT virtual orbitals
- INCAR.DFT.all
System = SrVO3 ISMEAR = -5 EMIN = -20 ; EMAX = 20 ; NEDOS = 1000 # usefull energy range for density of states ALGO = Exact ; NELM = 1 # exact diagonalization one step suffices EDIFF = 1E-8 # high precision for groundstate calculation NBANDS = 96 # need for a lot of bands in GW LOPTICS = .TRUE. # we need d phi/ d k for GW calculations KPAR = 3
Copy the aforementioned file to INCAR:
cp INCAR.DFT.all INCAR
and restart VASP.
The GW calculation
- INCAR.GW0
System = SrVO3 ISMEAR = -5 EMIN = -20 ; EMAX = 20 ; NEDOS = 1000 # usefull energy range for density of states NBANDS = 96 # need for a lot of bands in GW ALGO = GW0 # NELM = 1 # one step so this is really G0W0 PRECFOCK = Fast # select fast mode for FFT's ENCUTGW = 100 # energy cutoff for response function NOMEGA = 200 # metal, we need a lot of frequency points MAXMEM = 2500 # memory per core NKRED = 2 # sample down the GW to a coarse 2x2x2 grid KPAR = 3
Copy the aforementioned file to INCAR:
cp INCAR.GW0 INCAR
Analysis of the DOS
Again, add the following line to your INCAR file:
LORBIT = 11
and rerun VASP.
To plot the total DOS and the Vanadium t2g and eg partial-DOS using gnuplot, execute the following command:
./plotdos
Mind: Check the OUTCAR file for the position of the Fermi level. These DOSs have not been shifted such that the Fermi level is at 0 eV.
Bandstructure using WANNIER90
Again, add the following line to your INCAR to have VASP call WANNIER90:
LWANNIER90_RUN = .TRUE.
and use the following WANNIER90 input:
- wannier90.win.gw
bands_plot = true begin kpoint_path R 0.50000000 0.50000000 0.50000000 G 0.00000000 0.00000000 0.00000000 G 0.00000000 0.00000000 0.00000000 X 0.50000000 0.00000000 0.00000000 X 0.50000000 0.00000000 0.00000000 M 0.50000000 0.50000000 0.00000000 M 0.50000000 0.50000000 0.00000000 G 0.00000000 0.00000000 0.00000000 end kpoint_path num_wann = 3 num_bands= 3 exclude_bands : 1-20, 24-96 begin projections V:dxy;dxz;dyz end projections
Copy the above to wannier90.win:
cp wannier90.win.gw wannier90.win
and redo the GW step.
The compare the Vanadium t2g band dispersion in the GW approximation with the LDA bandstructure, run the following command:
gnuplot -persist plotme.gw
Mind: Here the eigenvalues have been shifted such that the Fermi level is a 0 eV.
A more accurate GW calculation
As you might have noticed in the previous example the Vanadium t2g bands look a bit wobbly along G-X and X-M. This turns out to be an artifact of the downsampling of the GW. Try removing (or comment out) the line
NKRED = 2
from the INCAR file, and redo the GW step.
Download
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