20.2.2 Frozen-core orbitals

CORE, $n_1,n_2,\ldots,$record.file;

$n_i$ is the number of frozen-core orbitals in irrep number $i$. These orbitals are doubly occupied in all configurations and not optimized.

record.file is the record name for frozen core orbitals; if not supplied, taken from orb on START card. record.file can be specified in any field after the last nonzero $n_i$. It should always be given if the orbital guess is from a neighbouring geometry and should then specify the SCF orbitals calculated at the present geometry. If a subsequent gradient calculation is performed with this wavefunction, record.file is mandatory and must specify closed-shell SCF orbitals at the present geometry. Note that record must be larger than 2000.

If the CORE card is omitted, then the numbers of core orbitals are taken from the most recent MCSCF calculation, or otherwise no orbitals are frozen. If the CORE card is given as CORE,record.file, then the orbitals corresponding to atomic inner shells are taken, i.e., $1s$ for Li-Ne, $1s2s2p$ for Na-Ar, etc. A CORE card without any specification resets the number of frozen core orbitals to zero.