Studies of molecular states using spin-coupled valence-bond theory

Abstract

The spin-coupled wavefunction for an N-electron system is described, and the technical aspects (formation of density matrices, energy minimisation, generation of virtual orbitals) briefly outline. The physical interpretation provided by this model is illustrated by calculations on the potential-energy surface of the C⁺+ H₂ system. The spin-coupled theory is quantitatively refined at the spin-coupled valence-bond stage. Results for calculations on CH⁺, LiHe⁺ and BH⁺₂ are presented which show that, at least for these systems, chemical accuracy may be attained with 200–500 non-orthogonal ‘spin-coupled structures’(configuration state functions). Each eigenvector is dominated by one or two such structures, thus providing visuality without sacrificing accuracy.