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 of electronic excitation energies \(\Omega^{(n)}\). 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]
Keywords
Keyword descriptions
- SECTION_PARAMETERS: logical = F
Lone keyword:
T
Usage: &BSE .TRUE.
Activates BSE calculations. [Edit on GitHub]
- BSE_APPROX: enum = TDA
Usage: &BSE_APPROX TDA
Valid values:
TDA
The TDA is applied, i.e. B=0.ABBA
The ABBA-matrix is diagonalized, i.e. the TDA is not applied.BOTH
The BSE is solved within the TDA (B=0) as well as for the full ABBA-matrix.
Level of approximation applied to BSE calculations. Choose between Tamm Dancoff approximation (TDA) and diagonalization of the full ABBA-matrix. [Edit on GitHub]
- BSE_DEBUG_PRINT: logical = F
Lone keyword:
T
Usage: &BSE_DEBUG_PRINT .TRUE.
Activates debug print statements in the BSE calculation. [Edit on GitHub]
- BSE_DIAG_METHOD: enum = FULLDIAG
Usage: &BSE_DIAG_METHOD FULLDIAG
Valid values:
FULLDIAG
Fully diagonalizes the BSE matrices within the chosen level of approximation.ITERDIAG
Iterative diagonalization has not been implemented yet.
Method for BSE calculations. Choose between full or iterative diagonalization. [Edit on GitHub]
- ENERGY_CUTOFF_OCC: real = -2.72113839E+001 [eV]
Usage: ENERGY_CUTOFF_OCC 10.0
Removing 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. \(\epsilon_{\mathrm{HOMO}}-\epsilon_a>\mathtt{ENERGY\_CUTOFF\_OCC}\). Can be used to accelerate runtime and reduce memory consumption. [Edit on GitHub]
- ENERGY_CUTOFF_VIRT: real = -2.72113839E+001 [eV]
Usage: ENERGY_CUTOFF_VIRT 10.0
Removing 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. \(\epsilon_i-\epsilon_{\mathrm{LUMO}}>\mathtt{ENERGY\_CUTOFF\_VIRT}\). Can be used to accelerate runtime and reduce memory consumption. [Edit on GitHub]
- EPS_X: real = 1.00000000E-001
Usage: EPS_X 0.1
Threshold for printing contributions of singleparticle transitions, i.e. elements of the eigenvector \(X_{ia}^{(n)}\). [Edit on GitHub]
- NUM_PRINT_EXC: integer = 10
Usage: NUM_PRINT_EXC 10
Number of printed excitation energies. Does not affect computation time. [Edit on GitHub]
- SPIN_CONFIG: enum = SINGLET
Usage: SPIN_CONFIG TRIPLET
Valid values:
SINGLET
Computes singlet excitations.TRIPLET
Computes triplet excitations.
Choose between calculation of singlet or triplet excitation (cf. given Reference above). [Edit on GitHub]