Towards multireference equivalents of the G2 and G3 methods

Twelve multireference equivalents of the G2 and G3 methods using reduced Møller-Plesset orders were introduced. The performance of these equivalents was assessed on a slightly reduced G2-1 test set. It was shown that whereas single-reference Gn-type procedures aim to approximate large-basis-set QCISD(T) calculations through additivity approximations, the MR-Gn methods aim to approximate large-basis-set MRCI+Q results.