Coupled valence bond theory

In this Letter, the formulation and implementation of a parallel response property code for non-orthogonal, valence bond wavefunctions are described. Test calculations on benzene and cyclobutadiene show that the polarisability and magnetisability tensors obtained using valence bond theory are comparable to those obtained at the full π-CASSCF level of theory. The properties are a weighted average of those of its individual resonance structures. Resonance has no relevance for the polarisability and magnetisability.