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| the_closed_shell_ccsd_program [2023/01/30 22:46] – [Coupled-cluster, CCSD] hesselmann | the_closed_shell_ccsd_program [2024/01/08 13:24] (current) – external edit 127.0.0.1 |
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| CCSD calculations with KS orbitals are possible. Optionally, the ''H0'' option can be used to specify the zeroth-order Hamiltonian (see options above). If KS or other non-HF reference states (like the Brueckner determinant) are employed in the calculation of the triples (T) additional singles terms are computed. This can be switched on/off with the option ''TRIP_FIA=1/0''. If ''TRIP_FIA=1'' the second order singles energy is computed in the triples program and if greater in magnitude than ''THR_E2SING'' the additional terms will be computed. | CCSD calculations with KS orbitals are possible. Optionally, the ''H0'' option can be used to specify the zeroth-order Hamiltonian (see options above). If KS or other non-HF reference states (like the Brueckner determinant) are employed in the calculation of the triples (T) additional singles terms are computed, see J. D. Watts, J. Gauss, R. Bartlett [[https://doi.org/10.1063/1.464480|J. Chem. Phys.]] **98**, 8718 (1993). This can be switched on/off with the option ''TRIP_FIA=1/0''. If ''TRIP_FIA=1'' the second order singles energy is computed in the triples program and if greater in magnitude than ''THR_E2SING'' the additional terms will be computed. |
| ''THR_E2SING=1d-6'' is the default setting for this threshold, which can also be altered via giving this keyword as an option to the CCSD program. | ''THR_E2SING=1d-6'' is the default setting for this threshold, which can also be altered via giving this keyword as an option to the CCSD program. |
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