An assessment of the accuracy of multireference configuration interaction (MRCI) and complete-active-space second-order perturbation theory (CASPT2) for breaking bonds to hydrogen

Complete-active-space self-consistent field (CASSCF), complete-active-space second-order perturbation theory (CASPT2), and two restricted active-space variants of multireference configuration interaction are assessed for bond-breaking reactions in BH, HF and CH4 by comparison to the full configuration interaction limit. The best results are obtained by choosing the larger of the two active spaces for a given molecule.