Spin-coupled valence bond study of low-lying states of LiHe⁺

Abstract

The spin-coupled valence bond approach to electronic structure is applied to the ground state and low-lying excited states of the LiHe⁺ molecular ion using a universal even-tempered basis set of Slater-type functions. Using just 23 spin-coupled structures, we examine directly the quality of the virtual orbitals for describing the asymptotic separations between the excited states, and find these to be very good.

Compact wavefunctions consisting of 208 spatial configurations constructed from single and double-excitations of just two of the spin-coupled orbitals, provide a reasonably accurate description of at least the six lowestlying states. Strongly avoided crossings are observed between the third and fourth states at R ≈ 1·98 Å, and between the sixth and seventh states at R ≈ 2·91 Å.

It is found that the occasional problems due to linear dependence are most effectively circumvented by Schmidt orthogonalization of the offending orbitals.