BSE
Parameters for a calculation solving the Bethe-Salpeter equation (BSE) for electronic excitations. The full BSE \(\left( \begin{array}{cc}A & B\\B & A\end{array} \right)\) \(\left( \begin{array}{cc}\mathbf{X}^{(n)}\\\mathbf{Y}^{(n)}\end{array} \right) = \Omega^{(n)}\left(\begin{array}{cc}1&0\\0&-1\end{array}\right)\) \(\left(\begin{array}{cc}\mathbf{X}^{(n)}\\\mathbf{Y}^{(n)}\end{array}\right)\) enables, for example, the computation of electronic excitation energies \(\Omega^{(n)}\) as well as optical properties. The BSE can be solved by diagonalizing the full ABBA-matrix or by setting B=0, i.e. within the Tamm-Dancoff approximation (TDA). Preliminary reference: Eq. (35) in PRB 92, 045209 (2015); http://dx.doi.org/10.1103/PhysRevB.92.045209 [Edit on GitHub]
Subsections
Keywords
Keyword descriptions
- SECTION_PARAMETERS
Type: logical
Default: F
Lone keyword: T
Usage: &BSE .TRUE.Description: Activates BSE calculations.
- BSE_DEBUG_PRINT
Type: logical
Default: F
Lone keyword: T
Usage: BSE_DEBUG_PRINT .TRUE.Description: Activates debug print statements in the BSE calculation.
- BSE_DIAG_METHOD
Type: enum
Default: FULLDIAG
Usage: BSE_DIAG_METHOD FULLDIAGDescription: Method for BSE calculations. Choose between full or iterative diagonalization.
Valid values:
FULLDIAGFully diagonalizes the BSE matrices within the chosen level of approximation.ITERDIAGIterative diagonalization has not been implemented yet.
- ENERGY_CUTOFF_EMPTY
Type: real
Default: -2.72113839E+001 [eV]
Usage: ENERGY_CUTOFF_EMPTY 10.0Description: Remove all orbitals with indices a,b from A_ia,jb and B_ia,jb with energy difference to LUMO level larger than the given energy cutoff, i.e. \(\varepsilon_a\in[\varepsilon_{a=\text{LUMO}}^{GW},\varepsilon_{a=\text{LUMO}}^{GW}+E_\text{cut}^\text{empty}]\). Can be used to accelerate runtime and reduce memory consumption.
- ENERGY_CUTOFF_OCC
Type: real
Default: -2.72113839E+001 [eV]
Usage: ENERGY_CUTOFF_OCC 10.0Description: Remove all orbitals with indices i,j from A_ia,jb and B_ia,jb with energy difference to HOMO level larger than the given energy cutoff, i.e. \(\varepsilon_i\in[\varepsilon_{i=\text{HOMO}}^{GW}-E_\text{cut}^\text{occ},\varepsilon_{i=\text{HOMO}}^{GW}]\). Can be used to accelerate runtime and reduce memory consumption.
- EPS_X
Type: real
Default: 1.00000000E-001
Usage: EPS_X 0.1Description: Threshold for printing contributions of singleparticle transitions, i.e. elements of the eigenvectors \(X_{ia}^{(n)}\) and \(Y_{ia}^{(n)}\).
- NUM_PRINT_EXC
Type: integer
Default: 25
Usage: NUM_PRINT_EXC 25Description: Number of printed excitation levels with respective energies and oscillator strengths. Does not affect computation time.
- NUM_PRINT_EXC_DESCR
Type: integer
Default: 0
Usage: NUM_PRINT_EXC_DESCR 5Description: Number of excitation levels for which the exciton descriptors are computed. Negative or too large NUM_PRINT_EXC_DESCR defaults to NUM_PRINT_EXC.
- PRINT_DIRECTIONAL_EXC_DESCR
Type: logical
Default: F
Lone keyword: T
Usage: PRINT_DIRECTIONAL_EXC_DESCR .TRUE.Description: Activates printing of exciton descriptors per direction.
- SPIN_CONFIG
Type: enum
Default: SINGLET
Usage: SPIN_CONFIG TRIPLETDescription: Choose between calculation of singlet or triplet excitation (cf. given Reference above).
Valid values:
SINGLETComputes singlet excitations.TRIPLETComputes triplet excitations.
- TDA
Type: enum
Default: ON
Usage: TDA ONDescription: Level of approximation applied to BSE calculations. Choose between Tamm Dancoff approximation (TDA) and/or diagonalization of the full ABBA-matrix.
Valid values:
ONThe TDA is applied, i.e. B=0.OFFThe ABBA-matrix is diagonalized, i.e. the TDA is not applied.TDA+ABBAThe BSE is solved within the TDA (B=0) as well as for the full ABBA-matrix.
- USE_KS_ENERGIES
Type: logical
Default: F
Lone keyword: T
Usage: USE_KS_ENERGIES .TRUE.Description: Uses KS energies instead of GW quasiparticle energies.