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:
For a description of the various singles corrections see Mol. Phys. 111, 607 (2013).
- 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).
- 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.