29.1 Options for EOM

Normally, no further input is needed for the calculation of excitation energies.

EOM-CCSD amplitudes can be saved using SAVE=record.ifil. The vectors will be saved after every refreshing of the iteration space and at the end of the calculation. The calculation can be restarted from the saved vectors, if START=record.ifil is specified. The set of vectors to be computed can be different in old and restarted calculations. However, if both cards (SAVE and START) are specified and the records for saving and restarting are identical, the sets of vectors should be also identical, otherwise chaos. The identical SAVE and START records can be useful for potential energy surfaces calculations, see section 25.4.1.

By default, only excitation energies are calculated, since the calculation of properties is about two times as expensive, as the calculation of energies only. The one-electron properties and transition moments (expectation type, as defined in: J.F. Stanton and R.J. Bartlett, J. Chem. Phys., 98 7029 (1993)) can be calculated by adding TRANS=1 to EOM card. The CCSD ground state is treated as a special case. If RELAX option is specified in EXPEC card, also the relaxed one-electron density matrix is calculated for the ground state. (Currently, the relaxed CCSD density matrix is available for all-electron calculations only.) By default, dipole moments are calculated. Other required properties can be specified using EXPEC card. Excited state densities are saved, if DM card is present. For an example see section 25.4.2. If TRANS=2, transition moments among excited states are also calculated.

It is possible to make the program to converge to a vector, which resembles a specified singles vector. This option is switched on by FOLLOW=$n$ card (usually $n$=2 should be set). FOLLOW card should be always accompanied with EXFILE=record.ifil card, where record.ifil contains singles vectors from a previous calculation, see section 25.4.3.