A comparison of single-reference coupled-cluster and multi-reference configuration interaction methods for representative cuts of the H2S(1A′) potential energy surface

Three cuts of the H2S(1A′) potential energy surface, which correspond to the dissociation of a single S-H bond [cut (i)], the simultaneous, C2v-symmetric, dissociation of both S-H bonds [cut (ii)], and the C2v-symmetric minimum energy dissociation pathway leading to H2(X1Σg+) and S(3p41D) [cut (iii)], are examined with the conventional and completely renormalized (CR) coupled-cluster (CC) methods, and the multi-reference configuration interaction approach [MRCI(Q)]. The size extensive CR-CC method with singles, doubles, and non-iterative triples, termed CR-CC(2,3), provides the results of the MRCI(Q) quality for cuts (i) and (iii). To obtain a similar quality for cut (ii), the CR-CC(2,3) energy must be corrected for the effect of quadruply excited clusters.