View source for Bandstructure of Si in GW (VASP2WANNIER90)

{{Template:gw}}

== Task ==

Calculation of the bandstructure of Si in GW using the VASP2WANNIER90 interface.

----
'''Mind''': The procedure to compute bandstructure in GW using V2W is almost identical to the corresponding HSE one 
described in [[Si_bandstructure|Si bandstructure]].

'''Mind''': The standard procedure for GW calculations is described in 
[[Bandgap of Si in GW|Bandgap of Si in GW]].
----

== Step 1: a DFT groundstate calculation ==
Everything starts with a standard DFT groundstate calculation (in this case PBE).

*{{TAG|INCAR}}

 {{TAGBL|ISMEAR}} =  0
 {{TAGBL|SIGMA}}  =  0.05
 {{TAGBL|GGA}}    = PE


*{{TAG|KPOINTS}}
<pre>
4x4x4
 0
G
 4 4 4
 0 0 0
</pre>

*{{TAG|POSCAR}}
<pre>
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
</pre>

== Step 2: obtain DFT virtual orbitals ==
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
number of bands by means of the {{TAG|NBANDS}}-tag.
To obtain the corresponding {{FILE|WAVEDER}} file we additionally specify {{TAG|LOPTICS}}=.TRUE.

*{{TAG|INCAR}}

 {{TAGBL|ALGO}} = Exact
 {{TAGBL|NBANDS}}  = 64
 {{TAGBL|LOPTICS}} = .TRUE.
 {{TAGBL|NEDOS}} = 2000
     
 {{TAGBL|ISMEAR}} =  0
 {{TAGBL|SIGMA}}  =  0.05
 {{TAGBL|GGA}}    = PE

== Step 3: GW calculation including LWANNIER90 TAG==
Restart from the {{FILE|WAVECAR}} and {{FILE|WAVEDER}} files of the previous calculation, with

*{{TAG|INCAR}}

 ## Frequency dependent dielectric tensor including
 ## local field effects within the RPA (default) or
 ## 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 and {{TAGBL|LOPTICS}}=.TRUE.
 ## and a reasonable number of virtual states (see above)
 {{TAGBL|ALGO}} = GW0 ; {{TAGBL|LSPECTRAL}} = .TRUE. ; {{TAGBL|NOMEGA}} = 50
 #{{TAGBL|LRPA}} = .FALSE. 
 ## be sure to take the same number of bands as for
 ## the {{TAGBL|LOPTICS}}=.TRUE. calculation, otherwise the
 ## {{TAGBL|WAVEDER}} file is not read correctly
 {{TAGBL|NBANDS}} = 64
 ##VASP2WANNIER90
 {{TAGBL|LWANNIER90}}=.TRUE.

Use the wannier90.win file given below which contains all instructions needed to generate the
necessary input files for the WANNIER90 runs (wannier90.amn, wannier90.mmn, wannier90.eig). 

*wannier90.win
<pre>
num_wann=8
num_bands=8

exclude_bands 9-64

Begin Projections
Si:sp3
End Projections

dis_froz_max=9
dis_num_iter=1000

guiding_centres=true

# Bandstructure plot 
#restart         =  plot
#bands_plot      =  true
#begin kpoint_path
#L 0.50000  0.50000 0.5000 G 0.00000  0.00000 0.0000
#G 0.00000  0.00000 0.0000 X 0.50000  0.00000 0.5000
#X 0.50000  0.00000 0.5000 K 0.37500 -0.37500 0.0000
#K 0.37500 -0.37500 0.0000 G 0.00000  0.00000 0.0000
#end kpoint_path
#bands_num_points 40
#bands_plot_format gnuplot xmgrace

begin unit_cell_cart
     2.7150000     2.7150000     0.0000000
     0.0000000     2.7150000     2.7150000
     2.7150000     0.0000000     2.7150000
end unit_cell_cart

begin atoms_cart
Si       0.0000000     0.0000000     0.0000000
Si       1.3575000     1.3575000     1.3575000
end atoms_cart

mp_grid =     4     4     4

begin kpoints
     0.0000000     0.0000000     0.0000000
     0.2500000     0.0000000     0.0000000
     0.5000000     0.0000000     0.0000000
     0.2500000     0.2500000     0.0000000
     0.5000000     0.2500000     0.0000000
    -0.2500000     0.2500000     0.0000000
     0.5000000     0.5000000     0.0000000
    -0.2500000     0.5000000     0.2500000
     0.0000000     0.2500000     0.0000000
     0.0000000     0.0000000     0.2500000
    -0.2500000    -0.2500000    -0.2500000
    -0.2500000     0.0000000     0.0000000
     0.0000000    -0.2500000     0.0000000
     0.0000000     0.0000000    -0.2500000
     0.2500000     0.2500000     0.2500000
     0.0000000     0.5000000     0.0000000
     0.0000000     0.0000000     0.5000000
    -0.5000000    -0.5000000    -0.5000000
     0.0000000     0.2500000     0.2500000
     0.2500000     0.0000000     0.2500000
    -0.2500000    -0.2500000     0.0000000
    -0.2500000     0.0000000    -0.2500000
     0.0000000    -0.2500000    -0.2500000
     0.0000000     0.5000000     0.2500000
     0.2500000     0.0000000     0.5000000
    -0.2500000    -0.2500000     0.2500000
    -0.5000000    -0.2500000    -0.5000000
     0.2500000     0.5000000     0.0000000
     0.2500000    -0.2500000    -0.2500000
    -0.5000000    -0.5000000    -0.2500000
     0.0000000     0.2500000     0.5000000
    -0.2500000     0.2500000    -0.2500000
    -0.2500000    -0.5000000    -0.5000000
     0.5000000     0.0000000     0.2500000
    -0.5000000    -0.2500000     0.0000000
     0.0000000    -0.5000000    -0.2500000
    -0.2500000     0.0000000    -0.5000000
     0.2500000     0.2500000    -0.2500000
     0.5000000     0.2500000     0.5000000
    -0.2500000    -0.5000000     0.0000000
    -0.2500000     0.2500000     0.2500000
     0.5000000     0.5000000     0.2500000
     0.0000000    -0.2500000    -0.5000000
     0.2500000    -0.2500000     0.2500000
     0.2500000     0.5000000     0.5000000
    -0.5000000     0.0000000    -0.2500000
     0.0000000    -0.2500000     0.2500000
     0.2500000     0.0000000    -0.2500000
    -0.2500000    -0.2500000    -0.5000000
     0.2500000     0.5000000     0.2500000
     0.2500000    -0.2500000     0.0000000
    -0.5000000    -0.2500000    -0.2500000
     0.2500000     0.2500000     0.5000000
     0.0000000     0.2500000    -0.2500000
    -0.2500000    -0.5000000    -0.2500000
     0.5000000     0.2500000     0.2500000
    -0.2500000     0.0000000     0.2500000
     0.0000000     0.5000000     0.5000000
     0.5000000     0.0000000     0.5000000
     0.2500000    -0.2500000     0.5000000
     0.5000000     0.2500000    -0.2500000
    -0.5000000    -0.2500000    -0.7500000
     0.2500000    -0.5000000    -0.2500000
    -0.2500000     0.2500000    -0.5000000
end kpoints
</pre>


== Step 4: WANNIER90==

=== Compute Wannier functions ===

run wannier90: 

wannier90.x wannier90

This run generates the wannier90 standard output (wannier90.wout)
and the file wannier90.chk needed for the wannier interpolation (next step) 
 
=== Obtain bandstructure (Wannier interpolation) ===

Uncomment the bandstructure plot flags in wannier90.win and rerun (restart) wannier90:

wannier90.x wannier90

This run generates the following bandstructure files which can be visualized using xmgrace or gnuplot:

wannier90_band.agr

wannier90_band.dat

wannier90_band.gnu

to plot the band structure using gnuplot:
<code>gnuplot -persist wannier90_band.gnu</code>

== Download ==
[http://www.vasp.at/vasp-workshop/examples/Si_bandstructure_GW.tgz Si_bandstructure_GW.tgz]
 
{{Template:gw}}

Back to the [[The_VASP_Manual|main page]].

[[Category:Examples]]