25.1 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 on the EXPEC card, also the relaxed one-electron density matrix is calculated for the ground state. (Currently, the relaxed CCSD density matrix through the EOM program is available for all-electron calculations only.) By default, dipole moments are calculated. Other required properties can be specified using EXPEC card. Properties are saved in MOLPRO variables, e.g. the $x$-component of the dipole moment is saved in DMX, its pure electron part in DMXE, transition moment – in TRDMX (left and right transition moments are stored separately). If DENSAVE=record.ifil is specified, excited-state densities are saved to record.ifil, otherwise they are saved to the record given in DM card. If TRANS=2, transition density matrices from/to the ground state will be saved provided that DENSAVE=record.ifil or DM card are specified and nonzero. If TRANS=3, transition moments among excited states are also calculated, and finally if TRANS=4, all transition densities will be saved (note that the last option should be used with caution because the number of densities to be stored will quickly exceed the allowed maximum). For an example see section 25.4.2.

When properties are needed, the left EOM-CCSD wave functions are calculated first. It is possible to use them as starting guesses for the right EOM-CCSD wave functions. This option is controlled by STARTLE (default 0). If STARTLE=1, left vectors are just used as a start for right vectors; if STARTLE=2, starting vectors, obtained from the left vectors are additionally biorthogonalized to the left vectors; finally, if STARTLE=3, also the final right vectors are biorthogonalized to the left vectors. The last possibility is of particular importance for degenerate states.

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.

molpro@molpro.net 2019-09-18