Electronic structure of Li3

Non-orthogonal single- and multi-configuration ab initio calculations have been carried out on ground-state Li-3 in its minimum-energy C-2v geometry. Their results have been compared with published work and with those of SCF, frozen-core SDCI and full-valence Cl calculations. The calculations confirm the feasibility of explicit basis-set optimisation, by second-order analytical methods, for correlated wavefunctions in non-linear molecules, and compare use of optimised STO basis sets with standard, high-accuracy, GTO basis sets. The results are used as basis for a discussion of the molecule's electronic structure. The molecule's electron density is shown to exhibit a non-nuclear maximum, both at the SCIF and frozen-core full-Cl levels, and with core-correlated non-orthogonal wavefunctions. An 'Atoms-in-Molecules' topological analysis of the electron density shows features that may be viewed as related to the occurrence of Interstitial Orbitals in non-orthogonal electronic wavefunctions for this system. The electron density difference map (molecule minus atoms) exhibits a non-nuclear maximum at roughly the same location as the molecule's total electron density, plus three 3p-type enrichment-depletion patterns, one centred on each nucleus. Corresponding patterns are found in Li-2. Li-3's electric dipole and electric field gradient at the nuclei are also computed. Unexpectedly, the electric dipole value is found to exhibit significant dependence on the inclusion of inner-shell out-of-plane correlation in the wavefunction. (C) 2008 Elsevier B.V. All rights reserved.