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Table of Contents

Overview
BSE Input directives

NROOT

Sample Input File
References

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BSE

Overview

Bethe–Salpeter equation

BSE input is provided using the compound directive

BSE
  ...
END

The actual BSE calculation will be performed when the input module encounters the TASK directive.

TASK DFT BSE

Note that DFT must be specified as the underlying QM theory before BSE. The charge, geometry, and DFT options are all specified as normal.

A BSE calculation requires not only a DFT ground state calculation, but a GW task to be executed, too.

BSE Input directives

There are sub-directives which allow for customized BSE calculations. The most general BSE input block directive will look like:

BSE
  NROOTS [<integer nroots default 10>]
  METHOD [ (davidson || analytic || lanczos) default analytic ]
  (SINGLET || TRIPLET) default SINGLET 
  TDA
  NCAP
  NCAPR
  OUTWIN
  MAXROOTS [<integer maxroots default 200>]
  SKIPGW
  MAXITER [<integer maxiter default 100>]
  NSTART
END

The following sections describe these keywords.

NROOT

The keyword NROOT

Sample Input File


geometry
H 0.000000 0.923274 1.238289
H 0.000000 -0.923274 1.238289
H 0.000000 0.923274 -1.238289
H 0.000000 -0.923274 -1.238289
C 0.000000 0.000000 0.668188
C 0.000000 0.000000 -0.668188
end

basis "ao basis" spherical bse
 * library aug-cc-pvdz
end

basis "ri basis" spherical bse
 * library aug-cc-pvdz-rifit
end

dft
  direct
  xc pbe0
  tolerances acccoul 10
  convergence energy 1d-8
  grid fine
end

gw
  evgw 5
  method analytic
  states alpha occ -1 vir -1
end

task gw

bse
 nroots 12
 method davidson
end

task bse