24.7.1 Parameters for EOM-CCSD (EOMPAR)

Normally, no further input is needed. However, some defaults can be changed using the EOMPAR directive:

EOMPAR, key1=value1, key2=value2,...

where the following keywords key are possible:

MAXDAV=nv

Maximum value of expansion vectors per state in Davidson procedure (default 10).

INISINGL=ns

Number of singly excited configurations to be included in initial Hamiltonian (default 20; the configurations are ordered according to their energy). Sometimes INISINGL should be put to zero in order to catch states dominated by double excitations.

INIDOUBL=nd

Number of doubly excited configurations to be included in initial Hamiltonian (default 10).

INIMAX=nmax

Maximum number of excited configurations to be included in initial Hamiltonian. By default, $nmax=ns+nd$.

MAXITER=itmax

Maximum number of iterations in EOM-CCSD (default 20).

MAXEXTRA=maxex

Maximum number of extra configurations allowed to be included in initial Hamiltonian (default 0). In the case of near degeneracy it is better to include a few extra configurations to avoid a slow convergence.

DIFOCK=difo

If set to 0, the program uses an approximate diagonal of ${\bar H}$ for looking for the initial configurations (corresponding to the $nmax+maxex$ lowest diagonal elements) and for the vector update in the Davidson procedure. If set to 1, the diagonal of the Fock matrix is used instead. If set to 2, the update procedures from CCSD program are used. DIFOCK=1 and 2 should give exactly the same results. Default for non-local EOM-CCSD (even based on local CCSD) is 0. For the local EOM-CCSD DIFOCK is always set to 2.

EOMLOCAL=eoml

If set to 0, non-local calculation (default). If set to 1, it simulates the local EOM-CCSD using the standard EOM program. EOMLOCAL=1 is a test option and shouldn't be used for the time being.

INIMAX is used only if INISINGL and INIDOUBL are both zero.

All keywords can be abbreviated by at least four characters.