Potential energy surfaces for H + Li2 → LiH + Li ground state surface from large scale configuration interaction

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Abstract
Ab initio electronic structure calculations have been performed to determine the HLi2 potential energy surface. A contracted Gaussian basis set was employed: H(5s 1p/3s 1p), Li(8s 3p/4s 3p). In addition to selfconsistent‐field (SCF) wavefunctions, full configuration interaction (CI) was carried out for the three valence electrons. For general geometry (point group Cs), the CI included 5175 configurations. For the diatomic molecules Li2 and LiH, these methods yield dissociation energies within 5 kcal/mole of experiment, and accurate spectroscopic constants are also predicted. The minimum on the HLi2 CI potential surface occurs for an isosceles triangle structure with r (H–Li) = 1.72 Å and on LiHLi bond angle of 95°. This minimum lies 22.4 kcal/mole below the separated products LiH + Li. The linear HLiLi minimum is much shallower, lying only 4.2 kcal/mole below the products. The much simpler single configuration SCF calculations yield qualitatively similar results. Furthermore, these features of the surface are quite analogous to those predicted for F + Li2 by Pearson and coworkers. The angular dependence of the surface between the C2v and C∞v extremes is discussed. The ’’electron jump’’ from covalent HLi2 to ionic H−Li2+ is seen to be much more gradual than was the case for FLi2. The electronic structure is described using a natural orbital analysis of the most important configurations in the wavefunction.