26.4 Modified Fock-operators in the zeroth-order Hamiltonian.

The $g_1$, $g_2$, and $g_3$ operators proposed by Andersson [Theor. Chim. Acta 91, 31 (1995)] as well as a further $g_4$ operator may be used. $g_4$ makes CASPT2 calculations size extensive for cases in which a molecule dissociates to high-spin open-shell (RHF) atoms.

The index n of the operator to be used is specified on the RS2, RS2C, or RS3 card:

RS2,option
RS2C,option
RS3,option

where option can be G1, G2, G3, or G4. This option can be followed or preceded by other valid options.