Plot BSE fatbands: Difference between revisions

From VASP Wiki
No edit summary
No edit summary
Line 1: Line 1:
It can be useful to inspect which electron-hole pairs contribute the most to a particular BSE eigenvector. In VASP it is possible to write the lowest {{TAG|NBSEEIG}} eigenvectors into a {{FILE|BSEFATBAND}} file, which can be used for making a fatband structure plot.
It can be useful to inspect which electron-hole pairs contribute the most to a particular BSE eigenvector {{cite|bokdam:scr:2016}}. In VASP it is possible to write the lowest {{TAG|NBSEEIG}} eigenvectors into the {{FILE|BSEFATBAND}} file, which can be used for making a fatband structure plot.


For example, a fatband structure plot for the first bright exciton can be made following these steps:
For example, a fatband structure plot for the first bright exciton can be made following these steps:
# Perform a [[Bethe-Salpeter-equations calculations|BSE]] calculation with {{TAG|NBSEEIG}} sufficiently large to include the exciton of interest.
# Perform a [[Bethe-Salpeter-equations calculations|BSE]] calculation with {{TAG|NBSEEIG}} sufficiently large to include the exciton of interest.
# Find the energy of the first bright exciton in {{FILE|vasprun.xml}} (''<varray name="opticaltransitions" >'')
# Find the energy of the first bright exciton in {{FILE|vasprun.xml}}, i.e., the first transition with non-zero oscillator strength (''<varray name="opticaltransitions" >'')
# Find the BSE eigenvector corresponding to this transition in the {{FILE|BSEFATBAND}} file.
# Find the BSE eigenvector corresponding to this transition in the {{FILE|BSEFATBAND}} file.
# Extract the coupling coefficients ''Abs(X_BSE)'' (Column 6) and energies (Column 4 and 5) corresponding to k points (Columns 1-3) along high-symmetry paths.
# Extract the coupling coefficients ''Abs(X_BSE)'' (Column 6) and energies (Column 4 and 5) corresponding to k points (Columns 1-3) along high-symmetry paths.
Line 25: Line 25:
  awk < BSE-$NBSE.dat '{ if ($1==$3 && $2==0.0) print sqrt($1*$1+$2*$2+$3*$3), $4, $5, $6}' > bands-GX.dat
  awk < BSE-$NBSE.dat '{ if ($1==$3 && $2==0.0) print sqrt($1*$1+$2*$2+$3*$3), $4, $5, $6}' > bands-GX.dat


[[File:Bsefatband.png|300px|thumb|The fatband structure plot of a BSE eigenvector in Si]]


The fatband structure plot can be produced in gnuplot by running the script:
The fatband structure plot can be done in gnuplot by running the following script:


  set size 0.5,1
  set size 0.5,1
Line 35: Line 36:
  set xrange[-0.866025:0.707107]
  set xrange[-0.866025:0.707107]
  M=0.001
  M=0.001
  p "bands-GL.dat" u (-$1):2:(M*($4)) w circles lc rgb "#2C68FC", \
   
  p "bands-GL.dat" u (-$1):2:(M*($4)) w circles lc rgb "#2C68FC", \
                 "" u (-$1):3:(M*($4)) w circles lc rgb "#A82C35", \
                 "" u (-$1):3:(M*($4)) w circles lc rgb "#A82C35", \
                 "" u (-$1):2 ps 0.5 lc "#808080" w d,  \
                 "" u (-$1):2 ps 0.5 lc "#808080" w d,  \
Line 47: Line 49:




[[File:Bsefatband.png|500px|caption="ssdfsdf"]]
== Related tags and sections ==
{{FILE|BSEFATBAND}}, {{FILE|NBSEEIG}}, [[Bethe-Salpeter-equations calculations|BSE]]
 
== References ==
<references/>
 
[[Category:VASP]][[Category:Many-body perturbation theory]][[Category:Bethe-Salpeter equations]]

Revision as of 16:36, 20 July 2022

It can be useful to inspect which electron-hole pairs contribute the most to a particular BSE eigenvector [1]. In VASP it is possible to write the lowest NBSEEIG eigenvectors into the BSEFATBAND file, which can be used for making a fatband structure plot.

For example, a fatband structure plot for the first bright exciton can be made following these steps:

  1. Perform a BSE calculation with NBSEEIG sufficiently large to include the exciton of interest.
  2. Find the energy of the first bright exciton in vasprun.xml, i.e., the first transition with non-zero oscillator strength (<varray name="opticaltransitions" >)
  3. Find the BSE eigenvector corresponding to this transition in the BSEFATBAND file.
  4. Extract the coupling coefficients Abs(X_BSE) (Column 6) and energies (Column 4 and 5) corresponding to k points (Columns 1-3) along high-symmetry paths.
  5. Plot the band structure with point size corresponding to the coupling coefficients Abs(X_BSE), i.e.,
|k-point|   electron        hole       Abs(X_BSE)
           eigenvalue    eigenvalue
    x          y1            y2        circle radius

You can use the following script for extracting the NBSE eigenvector along G-L and G-X directions in Si:

#!/bin/bash
#Select the BSE eigenvector of interest.
NBSE=1 
# The BSE product basis size.
BSIZE=$(head -n 1 BSEFATBAND | awk '{print $1}') 
i=`echo "($BSIZE+1)*$NBSE+1" | bc`
#Cut out the selected eigenstate.
head -n $i BSEFATBAND | tail -n $BSIZE > BSE-$NBSE.dat
awk < BSE-$NBSE.dat '{ if ($1==$2 && $3==$2)  print sqrt($1*$1+$2*$2+$3*$3), $4, $5, $6}' > bands-GL.dat
awk < BSE-$NBSE.dat '{ if ($1==$3 && $2==0.0) print sqrt($1*$1+$2*$2+$3*$3), $4, $5, $6}' > bands-GX.dat
The fatband structure plot of a BSE eigenvector in Si

The fatband structure plot can be done in gnuplot by running the following script:

set size 0.5,1
set nokey
set ylabel "Energy (eV)"
set yrange[-7:21]
set xtics ("L" -0.866025, "Г" 0, "X" 0.707107)
set xrange[-0.866025:0.707107]
M=0.001

 p "bands-GL.dat" u (-$1):2:(M*($4)) w circles lc rgb "#2C68FC", \
               "" u (-$1):3:(M*($4)) w circles lc rgb "#A82C35", \
               "" u (-$1):2 ps 0.5 lc "#808080" w d,  \
               "" u (-$1):3 ps 0.5 lc "#808080" w d,  \
   "bands-GX.dat" u 1:2:(M*($4)) w circles lc rgb "#2C68FC", \
               "" u 1:3:(M*($4)) w circles lc rgb "#A82C35",  \
               "" u 1:2 ps 0.5 lc "#808080" w d,      \
               "" u 1:3 ps 0.5 lc "#808080" w d



Related tags and sections

BSEFATBAND, NBSEEIG, BSE

References