Coupled valence bond theory

In this Letter, the formulation and implementation of a parallel response property code for non-orthogonal, valence bond wave-functions 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 p-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.