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Difference between revisions of "Plotting the BSE fatband structure of Si"

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(Step 2 BSE calculation with fatbands)
Line 88: Line 88:
 
The first number column shows the BSE eigenvalue and the second one the oscillator strength. We want to plot the first "bright" state, that means in this case number 4.
 
The first number column shows the BSE eigenvalue and the second one the oscillator strength. We want to plot the first "bright" state, that means in this case number 4.
  
 +
*We inspect the fourth band in the {{TAG|BSEFATBAND}} output file:
 +
              28428                10
 +
      1BSE eigenvalue    3.14798542      IP-eigenvalue:    3.25790292
 +
  0.00000  0.00000  0.00000    -6.1302666    9.0994773      0.0000001    1    5    -0.000000+i*    -0.000000
 +
  0.00000  0.00000  0.00000    5.8415744    9.0994773      0.0876503    2    5      0.000076+i*    0.000043
 +
  0.00000  0.00000  0.00000    5.8415744    9.0994773    341.0850802    3    5      0.088630+i*    -0.329369
 +
  0.00000  0.00000  0.00000    5.8415744    9.0994773    543.1678695    4    5      0.361803+i*    -0.405130
 +
  0.00000  0.00000  0.00000    -6.1302666    9.0994773      0.0000004    1    6    -0.000000+i*    0.000000
 +
…(28428-6 more lines till 2BSE eigenvalue …)
 +
      4BSE eigenvalue    3.14855812      IP-eigenvalue:    3.25790292
 +
  0.00000  0.00000  0.00000    -6.1302666    9.0994773      0.0024165    1    5      0.000002+i*    0.000001
 +
  0.00000  0.00000  0.00000    5.8415744    9.0994773      31.4738813    2    5    -0.027821+i*    -0.014718
 +
  0.00000  0.00000  0.00000    5.8415744    9.0994773    187.8684774    3    5      0.049093+i*    -0.181341
 +
  0.00000  0.00000  0.00000    5.8415744    9.0994773    360.1697144    4    5      0.239775+i*    -0.268757
 +
  0.00000  0.00000  0.00000    -6.1302666    9.0994773      0.0289534    1    6      0.000019+i*    -0.000022
 +
...
 +
 +
 
== Download ==
 
== Download ==
 
[http://www.vasp.at/vasp-workshop/examples/Si_BSEfatbands.tgz Si_BSEfatbands.tgz]
 
[http://www.vasp.at/vasp-workshop/examples/Si_BSEfatbands.tgz Si_BSEfatbands.tgz]

Revision as of 15:42, 14 December 2017

Task

Visualization of BSE eigenvectors using fatbands.

Input

Si
 5.4300
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 

INCAR

  • This is the INCAR file for the basic DFT calculation:
System  = Si

PREC = Normal ; ENCUT = 250.0

ISMEAR = 0 ; SIGMA = 0.01
KPAR = 2

EDIFF = 1.E-8
NBANDS = 16
LOPTICS = .TRUE.  # needed for WAVEDER file
LPEAD = .TRUE.
OMEGAMAX = 40

KPOINTS

The KPOINTS file will be automatically generated in this example.


Calculation

  • In this example we will calculate and plot the first "bright" BSE eigenstates of silicon, also called fatbands[1]. In this tutorial the modelBSE setup from the previous tutorial is used in combination with a gamma centered k-point grid (if you don't want to wait that long, a grid takes only a minute). In principle the standard BSE method can also be used instead.

Step 1 DFT calculation

We run a standard DFT calculation with the input files given above.

Step 2 BSE calculation with fatbands

  • The INCAR file for the modelBSE calculation looks like the following:
System  = Si

PREC = Normal ; ENCUT = 250.0

#ALGO = BSE 
ANTIRES = 0
ISMEAR = 0 ; SIGMA = 0.01
ENCUTGW = 150

EDIFF = 1.E-8 # default 1.E-4
NBANDS = 16   # only bands that are used are required, prepare the same set in a forgoing DFT run
NBANDSO = 4
NBANDSV = 8
OMEGAMAX = 20

PRECFOCK = Normal

ALGO = TDHF
LMODELHF = .TRUE. #Turn model on 
HFSCREEN = 1.26  # Screening lenght
AEXX = 0.088    #Inverse of epsilon_infinity
SCISSOR = 0.69  # Difference GW-DFT band gap

NBSEEIG = 10 # number of BSE eigenvectors written out in BSEFATBAND
  • The important tag for fatband calculations is NBSEEIG. In this example this will write the 10 energetically lowest BSE eigenvectors to the output file BSEFATBAND.
  • After the (model)BSE calculation we first look into the vasprun.xml file to have a look at the BSE eigenvalues and the oscillator strengths:

vasprun.xml (exact numbers can of course differ depending on the method you use and the density of your k-point grid):

<varray name="opticaltransitions" >
 <v>      3.148           0.000 </v>
 <v>      3.148           0.000 </v>
 <v>      3.148           0.000 </v>
 <v>      3.149       25654.244 </v> 
 <v>      3.149       25660.601 </v>
 <v>      3.149       25665.652 </v>
 <v>      3.151           0.001 </v>
 <v>      3.151           0.001 </v>
 <v>      3.152         423.751 </v>
 <v>      3.310      216931.963 </v>
 <v>      3.310      216916.814 </v>
 <v>      3.310      216935.593 </v>

The first number column shows the BSE eigenvalue and the second one the oscillator strength. We want to plot the first "bright" state, that means in this case number 4.

  • We inspect the fourth band in the BSEFATBAND output file:
             28428                10
     1BSE eigenvalue    3.14798542      IP-eigenvalue:    3.25790292
  0.00000  0.00000  0.00000    -6.1302666     9.0994773       0.0000001     1     5     -0.000000+i*    -0.000000
  0.00000  0.00000  0.00000     5.8415744     9.0994773       0.0876503     2     5      0.000076+i*     0.000043
  0.00000  0.00000  0.00000     5.8415744     9.0994773     341.0850802     3     5      0.088630+i*    -0.329369
  0.00000  0.00000  0.00000     5.8415744     9.0994773     543.1678695     4     5      0.361803+i*    -0.405130
  0.00000  0.00000  0.00000    -6.1302666     9.0994773       0.0000004     1     6     -0.000000+i*     0.000000
…(28428-6 more lines till 2BSE eigenvalue …)
     4BSE eigenvalue    3.14855812      IP-eigenvalue:    3.25790292
  0.00000  0.00000  0.00000    -6.1302666     9.0994773       0.0024165     1     5      0.000002+i*     0.000001
  0.00000  0.00000  0.00000     5.8415744     9.0994773      31.4738813     2     5     -0.027821+i*    -0.014718
  0.00000  0.00000  0.00000     5.8415744     9.0994773     187.8684774     3     5      0.049093+i*    -0.181341
  0.00000  0.00000  0.00000     5.8415744     9.0994773     360.1697144     4     5      0.239775+i*    -0.268757
  0.00000  0.00000  0.00000    -6.1302666     9.0994773       0.0289534     1     6      0.000019+i*    -0.000022
...


Download

Si_BSEfatbands.tgz

References


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