Electronic Structure of LiH Ion

Abstract

A valence-bond calculation has been carried out for (LiH)+ with all twenty structures possible from Slater orbitals 1s, 2s, 2p on lithium and 1s(=1h) orbital on hydrogen. The total electronic energy computed for the ion at the equilibrium distance for the LiH molecule is — 209.50 ev with only the 1s21h structure making a significant contribution to the ground state. When this energy is combined with the corresponding calculated energy for the molecule, a vertical ionization energy of 7.52 ev is obtained. No experimental value has as yet been reported. A technique is developed and is used to obtain the optimum orbital exponents for 1s21h over a wide range of internuclear distance. This calculated energy vs distance curve has no minimum suggesting that (LiH)+ is unstable with respect to dissociation. At R=3.08 au the wave function is ``degenerate,'' that is, two different extremum sets of exponents yield the same energy. The principal difference is that the orbital exponent of the 1h function is 0.49 in one set and 1.04 in the other. At R>3.08 au the second set gives the lowest energy while the reverse is true for R<3.08 au. This is interpreted as representing the promotion 1s→2s as is required in approaching the united atom.