Bandgap of Si in GW: Difference between revisions
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{{Template:GW - Tutorial}} | |||
'''Mind''': before you start doing GW calculations it might be beneficial to have a look at the examples on the [[ | == Task == | ||
Calculation of the bandgap of Si using various flavours of GW. | |||
---- | |||
'''Mind''': before you start doing GW calculations it might be beneficial to have a look at the examples on the [[Dielectric_properties_of_Si|description of dielectric properties]]. | |||
---- | ---- | ||
To do GW calculations we have to follow a 3-step procedure. | To do GW calculations we have to follow a 3-step procedure. | ||
== Step 1: | == Step 1: DFT groundstate calculation == | ||
Everything starts with a standard DFT groundstate calculation (in this case PBE). | Everything starts with a standard DFT groundstate calculation (in this case PBE). | ||
*{{TAG|INCAR}} (see INCAR.DFT) | *{{TAG|INCAR}} (see INCAR.DFT) | ||
ISMEAR = 0 | {{TAGBL|ISMEAR}} = 0 | ||
SIGMA = 0.05 | {{TAGBL|SIGMA}} = 0.05 | ||
EDIFF = 1E-8 | {{TAGBL|EDIFF}} = 1E-8 | ||
*{{TAG|KPOINTS}} (see KPOINTS.6) | *{{TAG|KPOINTS}} (see KPOINTS.6) | ||
| Line 48: | Line 51: | ||
== Step 2: obtain DFT virtual orbitals == | == Step 2: obtain DFT virtual orbitals == | ||
To obtain a {{FILE|WAVECAR}} file with a reasonable number of virtual orbitals (50-100 per atom) | To obtain a {{FILE|WAVECAR}} file with a reasonable number of virtual orbitals (50-100 per atom) | ||
we need to restart from the previous groundstate calculation with {{TAG|ALGO}}=Exact, and manually set the | we need to restart from the previous groundstate calculation with {{TAG|ALGO}}=''Exact'', and manually set the | ||
number of bands by means of the {{TAG|NBANDS}}-tag. | number of bands by means of the {{TAG|NBANDS}}-tag. | ||
To obtain the corresponding {{FILE|WAVEDER}} file we additionally specify {{TAG|LOPTICS}}=.TRUE. | To obtain the corresponding {{FILE|WAVEDER}} file we additionally specify {{TAG|LOPTICS}}=''.TRUE.''. | ||
*{{TAG|INCAR}} (see INCAR.DIAG) | *{{TAG|INCAR}} (see INCAR.DIAG) | ||
ISMEAR = 0 | {{TAGBL|ALGO}} = Exact | ||
SIGMA = 0.05 | {{TAGBL|NBANDS}} = 64 | ||
EDIFF = 1E-8 | {{TAGBL|LOPTICS}} = .TRUE. ; {{TAGBL|CSHIFT}} = 0.1 | ||
{{TAGBL|NEDOS}} = 2000 | |||
# you might try | |||
#{{TAGBL|LPEAD}} = .TRUE. | |||
{{TAGBL|ISMEAR}} = 0 | |||
{{TAGBL|SIGMA}} = 0.05 | |||
{{TAGBL|EDIFF}} = 1E-8 | |||
'''Mind''': make a copy of your {{FILE|WAVECAR}} and {{FILE|WAVEDER}} files, as we will repeatedly need them in the following. | '''Mind''': make a copy of your {{FILE|WAVECAR}} and {{FILE|WAVEDER}} files, as we will repeatedly need them in the following. | ||
For instance | For instance | ||
cp WAVECAR WAVECAR. | cp WAVECAR WAVECAR.DIAG | ||
cp WAVEDER WAVEDER. | cp WAVEDER WAVEDER.DIAG | ||
== Step 3: the actual GW calculation == | == Step 3: the actual GW calculation == | ||
| Line 76: | Line 79: | ||
*{{TAG|INCAR}} (see INCAR.GW) | *{{TAG|INCAR}} (see INCAR.GW) | ||
# Add this to update the quasiparticle energies | # Frequency dependent dielectric tensor including | ||
# in the Green's function (GW0) | # local field effects within the RPA (default) or | ||
#NELM = 4 | # including changes in the DFT xc-potential ({{TAGBL|LRPA}}=.FALSE.). | ||
# N.B.: beware one first has to have done a | |||
# calculation with {{TAGBL|ALGO}}=Exact, {{TAGBL|LOPTICS}}=.TRUE. | |||
# and a reasonable number of virtual states (see above) | |||
{{TAGBL|ALGO}} = GW0 ; {{TAGBL|LSPECTRAL}} = .TRUE. ; {{TAGBL|NOMEGA}} = 50 | |||
# be sure to take the same number of bands as for | |||
# the {{TAGBL|LOPTICS}}=.TRUE. calculation, otherwise the | |||
# WAVEDER file is not read correctly | |||
{{TAGBL|NBANDS}} = 64 | |||
# Add this to update the quasiparticle energies | |||
# in the Green's function (GW0) | |||
#{{TAGBL|NELM}} = 4 | |||
{{TAGBL|ISMEAR}} = 0 | |||
{{TAGBL|SIGMA}} = 0.05 | |||
{{TAGBL|EDIFF}} = 1E-8 | |||
At the bottom of the {{FILE|OUTCAR}} file you will find the quasi-particle (QP) energies. | At the bottom of the {{FILE|OUTCAR}} file you will find the quasi-particle (QP) energies. | ||
| Line 155: | Line 158: | ||
To include local field effects beyond the random-phase-approximation in the description of the frequency dependent dielectric response function (local field effects in DFT) add the following line to your {{FILE|INCAR}} file: | To include local field effects beyond the random-phase-approximation in the description of the frequency dependent dielectric response function (local field effects in DFT) add the following line to your {{FILE|INCAR}} file: | ||
LRPA = .FALSE. | {{TAGBL|LRPA}} = .FALSE. | ||
and again restart from the {{FILE|WAVECAR}} and {{FILE|WAVEDER}} files from step 2. | and again restart from the {{FILE|WAVECAR}} and {{FILE|WAVEDER}} files from step 2. | ||
| Line 164: | Line 167: | ||
To have VASP do, for instance, 4 iterations of the QP-energies in G, add the following line to the {{TAG|INCAR}} file: | To have VASP do, for instance, 4 iterations of the QP-energies in G, add the following line to the {{TAG|INCAR}} file: | ||
NELM = 4 | {{TAGBL|NELM}} = 4 | ||
and again restart from the {{FILE|WAVECAR}} and {{FILE|WAVEDER}} files from step 2. | and again restart from the {{FILE|WAVECAR}} and {{FILE|WAVEDER}} files from step 2. | ||
| Line 171: | Line 174: | ||
./gap_GW.sh OUTCAR | ./gap_GW.sh OUTCAR | ||
== | == Download == | ||
[[Media:Si GW gap.tgz| Si_GW_gap.tgz]] | |||
{{Template:GW - Tutorial}} | |||
Back to the [[The_VASP_Manual|main page]]. | |||
[[Category:Examples]] | [[Category:Examples]] | ||
Latest revision as of 11:10, 11 June 2024
Overview > bandgap of Si in GW > bandstructure of Si in GW (VASP2WANNIER90) > bandstructure of SrVO3 in GW > CRPA of SrVO3 > Equilibrium volume of Si in the RPA > List of tutorials
Task
Calculation of the bandgap of Si using various flavours of GW.
Mind: before you start doing GW calculations it might be beneficial to have a look at the examples on the description of dielectric properties.
To do GW calculations we have to follow a 3-step procedure.
Step 1: DFT groundstate calculation
Everything starts with a standard DFT groundstate calculation (in this case PBE).
- INCAR (see INCAR.DFT)
ISMEAR = 0 SIGMA = 0.05 EDIFF = 1E-8
- KPOINTS (see KPOINTS.6)
6x6x6 0 G 6 6 6 0 0 0
or to save some time use a "quick-and-dirty" setup (take KPOINTS.4):
4x4x4 0 G 4 4 4 0 0 0
system Si 5.430 0.5 0.5 0.0 0.0 0.5 0.5 0.5 0.0 0.5 2 cart 0.00 0.00 0.00 0.25 0.25 0.25
Step 2: obtain DFT virtual orbitals
To obtain a WAVECAR file with a reasonable number of virtual orbitals (50-100 per atom) we need to restart from the previous groundstate calculation with ALGO=Exact, and manually set the number of bands by means of the NBANDS-tag. To obtain the corresponding WAVEDER file we additionally specify LOPTICS=.TRUE..
- INCAR (see INCAR.DIAG)
ALGO = Exact NBANDS = 64 LOPTICS = .TRUE. ; CSHIFT = 0.1 NEDOS = 2000 # you might try #LPEAD = .TRUE. ISMEAR = 0 SIGMA = 0.05 EDIFF = 1E-8
Mind: make a copy of your WAVECAR and WAVEDER files, as we will repeatedly need them in the following.
For instance
cp WAVECAR WAVECAR.DIAG cp WAVEDER WAVEDER.DIAG
Step 3: the actual GW calculation
Restart from the WAVECAR and WAVEDER files of the previous calculation, with
- INCAR (see INCAR.GW)
# Frequency dependent dielectric tensor including # local field effects within the RPA (default) or # including changes in the DFT xc-potential (LRPA=.FALSE.). # N.B.: beware one first has to have done a # calculation with ALGO=Exact, LOPTICS=.TRUE. # and a reasonable number of virtual states (see above) ALGO = GW0 ; LSPECTRAL = .TRUE. ; NOMEGA = 50 # be sure to take the same number of bands as for # the LOPTICS=.TRUE. calculation, otherwise the # WAVEDER file is not read correctly NBANDS = 64 # Add this to update the quasiparticle energies # in the Green's function (GW0) #NELM = 4 ISMEAR = 0 SIGMA = 0.05 EDIFF = 1E-8
At the bottom of the OUTCAR file you will find the quasi-particle (QP) energies.
QP shifts <psi_nk| G(iteration)W_0 |psi_nk>: iteration 1
for sc-GW calculations column KS-energies equals QP-energies in previous step
and V_xc(KS)= KS-energies - (<T + V_ion + V_H > + <T+V_H+V_ion>^1 + <V_x>^1)
k-point 1 : 0.0000 0.0000 0.0000
band No. KS-energies QP-energies sigma(KS) V_xc(KS) V^pw_x(r,r') Z occupation
1 -6.4888 -6.8243 -10.9766 -10.4570 -17.5189 0.6458 2.0000
2 5.4800 5.1162 -11.8859 -11.4060 -12.7290 0.7580 2.0000
3 5.4800 5.1162 -11.8859 -11.4060 -12.7290 0.7580 2.0000
4 5.4800 5.1162 -11.8859 -11.4060 -12.7290 0.7580 2.0000
5 8.0443 8.3296 -9.7235 -10.1038 -5.7364 0.7502 0.0000
6 8.0443 8.3296 -9.7235 -10.1038 -5.7364 0.7502 0.0000
7 8.0443 8.3296 -9.7235 -10.1038 -5.7364 0.7502 0.0000
8 8.8407 9.2475 -10.5130 -11.0594 -6.0662 0.7445 0.0000
k-point 2 : 0.1667 0.0000 0.0000
band No. KS-energies QP-energies sigma(KS) V_xc(KS) V^pw_x(r,r') Z occupation
1 -6.1276 -6.4734 -11.0208 -10.4905 -17.3978 0.6521 2.0000
2 3.0946 2.6991 -11.4452 -10.9063 -13.1354 0.7340 2.0000
3 5.0279 4.6595 -11.7159 -11.2282 -12.6625 0.7552 2.0000
4 5.0279 4.6595 -11.7159 -11.2282 -12.6625 0.7552 2.0000
5 7.8309 8.1065 -9.8441 -10.2097 -5.8680 0.7539 0.0000
6 8.6943 8.9816 -9.8669 -10.2533 -5.6768 0.7436 0.0000
7 8.6943 8.9816 -9.8669 -10.2533 -5.6768 0.7436 0.0000
8 10.9341 11.2678 -10.4716 -10.9278 -5.5632 0.7316 0.0000
.. .. .. .. .. .. .. ..
.. .. .. .. .. .. .. ..
.. .. .. .. .. .. .. ..
.. .. .. .. .. .. .. ..
k-point 16 : -0.3333 0.5000 0.1667
band No. KS-energies QP-energies sigma(KS) V_xc(KS) V^pw_x(r,r') Z occupation
1 -2.2240 -2.5911 -11.4857 -10.9550 -16.0663 0.6917 2.0000
2 -2.2240 -2.5911 -11.4857 -10.9550 -16.0663 0.6917 2.0000
3 1.8279 1.3698 -10.7735 -10.1380 -12.9637 0.7209 2.0000
4 1.8279 1.3698 -10.7735 -10.1380 -12.9637 0.7209 2.0000
5 8.2346 8.4128 -9.3111 -9.5472 -5.1975 0.7546 0.0000
6 8.2346 8.4128 -9.3111 -9.5472 -5.1975 0.7546 0.0000
7 12.2605 12.5170 -9.7969 -10.1486 -4.3607 0.7294 0.0000
8 12.2605 12.5170 -9.7969 -10.1486 -4.3607 0.7294 0.0000
To quickly find the QP-energy of the highest lying occupied state, try
./gap_GW.sh OUTCAR
Beyond the random-phase-approximation
To include local field effects beyond the random-phase-approximation in the description of the frequency dependent dielectric response function (local field effects in DFT) add the following line to your INCAR file:
LRPA = .FALSE.
and again restart from the WAVECAR and WAVEDER files from step 2.
Beyond G0W0: GW0
The most usual step beyond single-shot GW (G0W0) is to iterate the quasi-particle energies in the Greens functions. This is the socalled GW0 approximation. To have VASP do, for instance, 4 iterations of the QP-energies in G, add the following line to the INCAR file:
NELM = 4
and again restart from the WAVECAR and WAVEDER files from step 2.
To quickly find the QP-energy of the highest lying occupied state after 4 iterations of the QP energies in G, type:
./gap_GW.sh OUTCAR
Download
Overview > bandgap of Si in GW > bandstructure of Si in GW (VASP2WANNIER90) > bandstructure of SrVO3 in GW > CRPA of SrVO3 > Equilibrium volume of Si in the RPA > List of tutorials
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