21.3 Additional reference symmetries

REF,sym;

This card, which must come after the WF directive, defines an additional reference symmetry used for generating the uncontracted internal and singly external configuration spaces. This is sometimes useful in order to obtain the same configuration spaces when different point group symmetries are used. For instance, if a calculation is done in $C_s$ symmetry, it may happen that the two components of a $\Pi$ state, one of which appears in $A'$ and the other in $A''$, come out not exactly degenerate. This problem can be avoided as in the following example:

for a doublet $A'$ state:

WF,15,1,1;      !define wavefunction symmetry (1)
REF,2;          !define additional reference symmetry (2)

and for the doublet A'' state:

WF,15,2,1;      !define wavefunction symmetry (2)
REF,1;          !define additional reference symmetry (1)

For linear geometries the same results can be obtained more cheaply using $C_{2v}$ symmetry,

WF,15,2,1;      !define wavefunction symmetry (2)
REF,1;          !define additional reference symmetry (1)
REF,3;          !define additional reference symmetry (3)

or

WF,15,3,1;      !define wavefunction symmetry (2)
REF,1;          !define additional reference symmetry (1)
REF,2;          !define additional reference symmetry (2)

Each REF card may be followed by RESTRICT, SELECT, and CON cards, in the given order.