View source for Bandgap of Si using different DFT+HF methods

{{Template:Hybrid_functionals - Tutorial}}

== Task ==

Calculation of the band gap in Si using different DFT+HF schemes [[list_of_hybrid_functionals|(PBE, B3LYP, PBE0, HSE06, and HF)]].

== Input ==

=== {{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
   1  
Cartesian
0    0    0
0.25 0.25 0.25
</pre>

=== {{TAG|INCAR}} ===

 ## Better preconverge with PBE first
 ## and use the WAVECAR file as inout for the DFT+HF calculation
    
 ## Selects the B3LYP hybrid functional
 #{{TAGBL|LHFCALC}} = .TRUE. ; {{TAGBL|GGA}} = B3 ; {{TAGBL|AEXX}} = 0.2 ; {{TAGBL|AGGAX}} = 0.72 
 #{{TAGBL|AGGAC}} = 0.81 ; {{TAGBL|ALDAC}} = 0.19
 #{{TAGBL|ALGO}} = D ; {{TAGBL|TIME}} = 0.4 
    
 ## Selects the PBE0  hybrid functional
 #{{TAGBL|LHFCALC}} = .TRUE. ; 
 #{{TAGBL|ALGO}} = D ; {{TAGBL|TIME}} = 0.4 
    
 ## Selects the HSE06 hybrid functional
 #{{TAGBL|LHFCALC}} = .TRUE. ; {{TAGBL|HFSCREEN}} = 0.2 ; 
 #{{TAGBL|ALGO}} = D ; {{TAGBL|TIME}} = 0.4 
    
 ## Selects HF 
 #{{TAGBL|LHFCALC}} = .TRUE. ; {{TAGBL|AEXX}} = 1.0 ; {{TAGBL|ALDAC}} = 0.0 ; {{TAGBL|AGGAC}} = 0
 #{{TAGBL|ALGO}} = D ; {{TAGBL|TIME}} = 0.4 
    
 ## Leave this in
 {{TAGBL|ISMEAR}} =  0
 {{TAGBL|SIGMA}}  =  0.01
 {{TAGBL|GGA}}    = PE
 

=== {{TAG|KPOINTS}} ===
<pre>
k-points
0
Gamma
  6  6  6
  0  0  0
</pre>

=== Calculation ===

*script to extract eigenvalues and calculate the bandgap
<pre>
homo=`awk '/NELECT/ {print $3/2}' $1`
lumo=`awk '/NELECT/ {print $3/2+1}' $1`
nkpt=`awk '/NKPTS/ {print $4}' $1`

e1=`grep "     $homo     " $1 | head -$nkpt | sort -n -k 2 | tail -1 | awk '{print $2}'`
e2=`grep "     $lumo     " $1 | head -$nkpt | sort -n -k 2 | head -1 | awk '{print $2}'`

echo "HOMO: band:" $homo " E=" $e1
echo "LUMO: band:" $lumo " E=" $e2
</pre>
:type
 ./gap.sh OUTCAR


*README.txt
<pre>
For each HF+DFT method (B3LYP, PBE0, HSE06, and HF) compute the bandgap of Si
adopting the following procedure:

i) Perform a standard PBE calculation
ii) Perform a HF+DFT run (VASP reads in the WAVECAR from run (i)
iii) Calculate the value of the bandgap by running the script 'gap': 
     bandgap = min(cband) - max(vband) 
</pre>

== Download ==
[[Media:Si hybrids gap.tgz| Si_hybrids_gap.tgz]]
 
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[[Category:Examples]]