CasidaTheoryLevel
CasidaTheoryLevel
Section Linear Response::Casida
Type flag
Default eps_diff + petersilka + lrtddft_casida
Choose which electron-hole matrix-based theory levels to use in calculating excitation energies.
More than one may be used to take advantage of the significant commonality between the calculations.
variational and lrttdft_casida are not usable with complex wavefunctions.
Note the restart data saved by each theory level is compatible with all the others.
Options:
- eps_diff:
Difference of eigenvalues, i.e. independent-particle approximation.
- petersilka:
The Petersilka approximation uses only elements of the Tamm-Dancoff matrix between degenerate
transitions (if no degeneracy, this is just the diagonal elements). Also called the "single-pole" approximation.
This is acceptable if there is little mixing between single-particle transitions.
Ref: M Petersilka, UJ Gossmann, and EKU Gross, Phys. Rev. Lett. 76, 1212 (1996);
T Grabo, M Petersilka,and EKU Gross, Theochem 501-502 353 (2000).
- tamm_dancoff:
The Tamm-Dancoff approximation uses only occupied-unoccupied transitions and not
unoccupied-occupied transitions.
Ref: S Hirata and M Head-Gordon, Chem. Phys. Lett. 314, 291 (1999).
- variational:
Second-order constrained variational theory CV(2)-DFT. Only applies to real wavefunctions.
Ref: T Ziegler, M Seth, M Krykunov, J Autschbach, and F Wang,
J. Chem. Phys. 130, 154102 (2009).
- lrtddft_casida:
The full Casida method. Only applies to real wavefunctions.
Ref: C Jamorski, ME Casida, and DR Salahub, J. Chem. Phys. 104, 5134 (1996)
and ME Casida, "Time-dependent density functional response theory for molecules,"
in Recent Advances in Density Functional Methods, edited by DE Chong, vol. 1
of Recent Advances in Computational Chemistry, pp. 155-192 (World Scientific,
Singapore, 1995).