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35.8 CABS Singles correction

By default, the perturbative CABS singles correction as described in J. Chem. Phys. 127, 221106 (2007) and J. Chem. Phys. 128, 154103 (2008) is included in the reference energy of all MP2-F12 and CCSD-F12 calculations (closed and open-shell, except for LMP2-F12/3*A(loc), which is done with a different program). The corrected reference energy is stored in variable ENERGR, so that ENERGY-ENERGR are the total correlation energies. For the setting of other variables by the F12 programs see section 35.12.

The singles correction can be turned off by option SINGLES=0, e.g.


The contribution of core orbitals to the singles energy is not included by default, but can be turned on by option CORE_SINGLES, e.g.


However, we do not recommended the use of core singles, because they depend sensitively on the CABS basis construction and do not offer significant improvements in relative energies. 2018-01-18