ABINIT, BSE input variables:

List and description.


This document lists and provides the description of the name (keywords) of the "BSE" input variables to be used in the main input file of the abinit code.


Copyright (C) 1998-2017 ABINIT group (DCA,XG,RC,YG,FJ)

Content of the file : alphabetical list of "BSE" variables.


A.
B. bs_algorithm   bs_calctype   bs_coulomb_term   bs_coupling   bs_eh_cutoff   bs_exchange_term   bs_freq_mesh   bs_hayd_term   bs_haydock_niter   bs_haydock_tol   bs_interp_kmult   bs_interp_m3_width   bs_interp_method   bs_interp_mode   bs_interp_prep   bs_interp_rl_nb   bs_loband   bs_nstates  



bs_algorithm
Mnemonics: Bethe-Salpeter ALGORITHM
Executable: abinit
Mentioned in topic: BSE.
Moderately used: [16/907] in abinit tests, [4/136] in tuto abinit tests. Tuto test list: {tutoparal:[mbt_5],tutorial:[bs_2,bs_3,bs_4]}.
Variable type: integer
Default is 2

Only relevant if optdriver == 99

The bs_algorithm input variable defines the algorithm employed to calculate the macroscopic dielectric function. Possible values are 1, 2 or 3:



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bs_calctype
Mnemonics: Bethe-Salpeter CALCulation TYPE
Executable: abinit
Mentioned in topic: BSE.
Moderately used: [16/907] in abinit tests, [4/136] in tuto abinit tests. Tuto test list: {tutoparal:[mbt_5],tutorial:[bs_2,bs_3,bs_4]}.
Variable type: integer
Default is 1

Only relevant if optdriver == 99

Possible values are 1,2,3.



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bs_coulomb_term
Mnemonics: Bethe-Salpeter COULOMB TERM
Executable: abinit
Mentioned in topic: BSE.
Moderately used: [16/907] in abinit tests, [4/136] in tuto abinit tests. Tuto test list: {tutoparal:[mbt_5],tutorial:[bs_2,bs_3,bs_4]}.
Variable type: integer
Default is 11

Only relevant if optdriver == 99

This variable governs the choice among the different options that are available for the treatment of Coulomb term of the Bethe-Salpeter Hamiltonian. bs_coulomb_term is the concatenation of two digits, labelled (A) and (B).

The first digit (A) can assume the values 0,1,2:

The second digit (B) can assume the values 0,1:



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bs_coupling
Mnemonics: Bethe-Salpeter COUPLING
Executable: abinit
Mentioned in topic: BSE.
Moderately used: [16/907] in abinit tests, [4/136] in tuto abinit tests. Tuto test list: {tutoparal:[mbt_5],tutorial:[bs_2,bs_3,bs_4]}.
Variable type: integer
Default is 0

Only relevant if optdriver == 99

The bs_coupling input variable defines the treatment of the coupling block of the Bethe-Salpeter Hamiltonian. Possible values are 0,1.



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bs_eh_cutoff
Mnemonics: Bethe-Salpeter Electron-Hole CUTOFF
Executable: abinit
Mentioned in topic: BSE.
Rarely used: [0/907] in abinit tests, [0/136] in tuto abinit tests.
Variable type: integer(2)
Default is [-inf, inf]

Only relevant if optdriver == 99

It is used to define a cutoff in the e-h basis set. Only those transitions whose energy is between bs_eh_window(1) and bs_eh_window(2) will be considered during the construction of the e-h Hamiltonian.



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bs_exchange_term
Mnemonics: Bethe-Salpeter EXCHANGE TERM
Executable: abinit
Mentioned in topic: BSE.
Moderately used: [16/907] in abinit tests, [4/136] in tuto abinit tests. Tuto test list: {tutoparal:[mbt_5],tutorial:[bs_2,bs_3,bs_4]}.
Variable type: integer
Default is 1

Only relevant if optdriver == 99



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bs_freq_mesh
Mnemonics: Bethe-Salpeter FREQuency MESH
Executable: abinit
Characteristic: ENERGY
Mentioned in topic: BSE.
Moderately used: [15/907] in abinit tests, [4/136] in tuto abinit tests. Tuto test list: {tutoparal:[mbt_5],tutorial:[bs_2,bs_3,bs_4]}.
Variable type: real(3)
Default is [0.0, 0.0, 0.01]

Only relevant if optdriver == 99

bs_freq_mesh(1) defines the first frequency for the calculation of the macroscopic dielectric function.

bs_freq_mesh(2) gives the last frequency for the calculation of the macroscopic dielectric function. If zero, bs_freq_mesh(2) is set automatically to MAX(resonant_energy) + 10%.

bs_freq_mesh(3) gives the step of the linear mesh used for evaluating the macroscopic dielectric function.



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bs_hayd_term
Mnemonics: Bethe-Salpeter HAYdock TERMinator
Executable: abinit
Mentioned in topic: BSE.
Rarely used: [7/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v67mbpt:[11,14,31,32,33,34,35]}.
Variable type: integer
Default is 1

Only relevant if optdriver == 99 and bs_algorithm==2

Defines how to terminate the continued fraction expression for the dielectric function. The terminator reduces the number of iterations needed to converge by smoothing the oscillation in the high energy part of the spectrum



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bs_haydock_niter
Mnemonics: Bethe-Salpeter HAYDOCK Number of ITERations
Executable: abinit
Mentioned in topic: BSE.
Moderately used: [13/907] in abinit tests, [4/136] in tuto abinit tests. Tuto test list: {tutoparal:[mbt_5],tutorial:[bs_2,bs_3,bs_4]}.
Variable type: integer
Default is 100

Only relevant if optdriver == 99 and bs_algorithm==2

bs_haydock_niter defines the maximum number of iterations used to calculate the macroscopic dielectric function. The iterative algorithm stops when the difference between two consecutive evaluations of the optical spectra is less than bs_haydock_tol.



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bs_haydock_tol
Mnemonics: Bethe-Salpeter HAYDOCK TOLerance
Executable: abinit
Mentioned in topic: BSE.
Moderately used: [11/907] in abinit tests, [4/136] in tuto abinit tests. Tuto test list: {tutoparal:[mbt_5],tutorial:[bs_2,bs_3,bs_4]}.
Variable type: real(2)
Default is [0.02, 0]

Only relevant if optdriver == 99 and bs_algorithm==2

Defines the convergence criterion for the Haydock iterative method. The iterative algorithm stops when the difference between two consecutive evaluations of the macroscopic dielectric function is less than bs_haydock_tol(1) . The sign of bs_haydock_tol(1) defines how to estimate the convergence error. A negative value signals that the converge should be reached for each frequency (strict criterion), while a positive value indicates that the converge error is estimated by averaging over the entire frequency range (mild criterion).

bs_haydock_tol(2) defines the quantity that will be checked for convergence:



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bs_interp_kmult
Mnemonics: Bethe-Salpeter INTERPolation K-point MULTiplication factors
Executable: abinit
Mentioned in topic: BSE.
Rarely used: [4/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v67mbpt:[32,33,34,35]}.
Variable type: integer(3)
Default is [0, 0, 0]

Only relevant if bs_interp_mode > 0 and bs_algorithm==2 and bs_coupling==0

bs_interp_kmult defines the number of divisions used to generate the dense mesh in the interpolation. ngkpt of the dense mesh = bs_interp_kmult(:) * ngkpt of the coarse mesh.



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bs_interp_m3_width
Mnemonics: Bethe-Salpeter INTERPolation Method3 WIDTH
Executable: abinit
Mentioned in topic: BSE.
Rarely used: [1/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v67mbpt:[34]}.
Variable type: real
Default is 1.0

Only relevant if bs_interp_mode==3 and bs_algorithm==2 and bs_coupling==0

Defines the width of the region where divergence treatment is applied for BSE interpolation

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bs_interp_method
Mnemonics: Bethe-Salpeter INTERPolation METHOD
Executable: abinit
Mentioned in topic: BSE.
Rarely used: [4/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v67mbpt:[32,33,34,35]}.
Variable type: integer
Default is 1

Only relevant if bs_interp_mode > 0 and bs_algorithm==2 and bs_coupling==0

bs_interp_method selects the method of interpolation:



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bs_interp_mode
Mnemonics: Bethe-Salpeter INTERPolation MODE
Executable: abinit
Mentioned in topic: BSE.
Rarely used: [4/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v67mbpt:[32,33,34,35]}.
Variable type: integer
Default is 0

Only relevant if bs_interp_mode > 0 and bs_algorithm==2 and bs_coupling==0

bs_interp_mode selects the mode of interpolation:



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bs_interp_prep
Mnemonics: Bethe-Salpeter INTERPolation PREParation
Executable: abinit
Mentioned in topic: BSE.
Rarely used: [1/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v67mbpt:[31]}.
Variable type: integer
Default is 0

Only relevant if bs_interp_mode > 0 and bs_algorithm==2 and bs_coupling==0

bs_interp_prep allows to trigger the preparation of the interpolation with method 2 or method 3. It generates the decomposition of BSR in a,b,c coefficients used for the interpolation.



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bs_interp_rl_nb
Mnemonics: Bethe-Salpeter INTERPolation Rohlfing & Louie NeighBour
Executable: abinit
Mentioned in topic: BSE.
Rarely used: [1/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v67mbpt:[35]}.
Variable type: integer
Default is 1

Only relevant if bs_interp_mode > 0 and bs_algorithm==2 and bs_interp_method == 1 and bs_coupling==0

Gives the index of the neighbour that is used for Rohlfing & Louie method

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bs_loband
Mnemonics: Bethe-Salpeter Lowest Occupied BAND
Executable: abinit
Mentioned in topic: BSE.
Moderately used: [16/907] in abinit tests, [4/136] in tuto abinit tests. Tuto test list: {tutoparal:[mbt_5],tutorial:[bs_2,bs_3,bs_4]}.
Variable type: integer(nsppol)
Default is 0

Only relevant if optdriver == 99

This variable defines the index of the lowest occupied band used for the construction of the electron-hole basis set. For spin polarized calculations, one must provide two separated indices for spin up and spin down. An additional cutoff energy can be applied by means of the bs_eh_window input variable.



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bs_nstates
Mnemonics: Bethe-Salpeter Number of STATES
Executable: abinit
Mentioned in topic: BSE.
Rarely used: [4/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v67mbpt:[11,16,29,50]}.
Variable type: integer
Default is 0

Only relevant if optdriver == 99 and bs_algorithm in [2,3]

bs_nstates defines the maximum number of excitonic states calculated in the direct diagonalization of the excitonic matrix or in the conjugate-gradient method. The number of states should be sufficiently large for a correct description of the optical properties in the frequency range of interest.



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