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** Next:** 20.2.7 Selecting configurations
** Up:** 20.2 Specifying the wavefunction
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20.2.6 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
symmetry, it may happen that the two components of a state, one of which
appears in and the other in , come out not exactly degenerate. This problem can be
avoided as in the following example:

for a doublet 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 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.

molpro@molpro.net 2018-06-21