Bethe-Salpeter
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In this tutorial
subheader
BSE Tutorials at present:
- SiH_4
- Fantastic dimension
- LiF
- you Hydrogen
- GaSb (SOC)
- hexagonal BN (on slides only)
The material
The h-BN is a layered material similar to graphite. It is an indirect wide band-gap material. Its optical spectrum is characterized by large excitonic effects. 5.95 eV is the minimum electronic indirect gap. 6.47 eV is the minimum direct gap. See the literature [1]
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Bulk hexagonal BN
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[[File:|Band Structure]] |
Calculate the screening
A key ingredient to construct the BS kernel in the Screeened EXchange approximation (sex) is the screened electron-electron dielectric matrix W which is normally evaluated in the static approximation.
You have two main options to generate the input :
1) yambo -b -F yambo_Ws.in
This will create the input to calculate W (database ndb.em1s)
2) yambo -p p -F yambo_Wp.in
This will create the input to calculate (or read) W in the PPA approximation (database ndb.pp) This second option is useful if you want to read the static part of W from a previous database ndb.pp generated in a GW-PPA run
Calculate the BS kernel in the SEX (Screened Exchange approximation) in the transitions space
Here we learn how to create the BS kernel in the screened exchange (SEX) approximation which includes both exchange (V) and correlation (-W) terms Runlevel to be used yambo -o b -k sex
Solve the BSE by haydock solver and and calculate spectrum
Generate the input file for solving the BSE using the Haydock solver:
yambo -o-y h
Solve the BSE by diagonalizing the excitonic matrix and calculate spectrum
Runlevel to be used yambo -y d
Steps:
-Calculate screening
-Calculate the BS Kernel
-Diagonalize the BS Matrix and calculate spectrum
-Visualize/Analyze excitons (with ypp)
-How to Converge
-How to work with SOC