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20.8 Explicitly correlated MRCI-F12

The only change needed for including explicitly correlated terms is to append -F12 to the MRCI command. All other options work as described before. It is recommended to use correlation consistent basis sets (aug-cc-pVnZ or VnZ-F12) since for these the appropriate fitting and RI auxiliary basis sets are chosen automatically. Otherwise it max be necessary to specify these basis sets as described for single-reference methods in section 35.

The following options (to be given on the MRCI-F12 command line) are specific to MRCI-F12:

SCALF12=scalf12
If scalf12=1 (default) the explicitly correlated contributions are treated variationally (SFIX ansatz, see J. Chem. Phys. 134, 034113 (2011). If scalf12=0 intermediate normalization is used (FIX ansatz).
SINGLES=isingles
isingles=1: use singles-CI CABS singles correction (default); isingles=2: use perturbational CABS singles correction; isingles=3: include couplings of CABS singles with MRCI terms.
For a description of the various singles corrections see Mol. Phys. 111, 607 (2013).

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