25.1 Options for

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 -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`= card (usually =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 2019-08-22