Bethe-Salpeter

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In this tutorial

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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]

Bulk hexagonal BN [2] hexagonal lattice Two atoms per cell (16 electrons) Lattice parameters a = 4.72 [a.u.] c/a= 2.58 Plane waves cutoff 40 Rydberg

[[File:|Band Structure]]

Calculate screening

A key ingredient in the construction of the BS kernel in the screeened exchange approximation (sex) is the screened electron-electron interaction W which is evaluated in the static approximation.

To create the input: yambo -b -F ./Inputs/05_W.in

To run : yambo -F ./Inputs/05_W.in

At the end of the run you will find a new database ndb.em1s. It will be in ./SAVE direcory if you did not use the -J option

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

Runlevel to be used yambo -y h

Solve the BSE by diagonalizing the excitonic matrix

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