Resonating Valence Bond calculations on small anionic lithium clusters

We recast the Resonating Valence Bond theory, first introduced bq Linus Pauling, in a nonorthogonal ab initio Valence Bond formalism and apply the method to study some properties of the anionic clusters Li-n(-) (2 less than or equal to n less than or equal to 5). We show how to choose appropriate structures and orbitals, and also how to use the so-called metallic orbitals. The problem of interpreting the role of a specific Valence Bond structure looking up its weight in the general wave function is elucidated. Information about the excited states of the systems is obtained. The theory can make good qualitative predictions on the electronic behaviour of the clusters by using a wave function that is a linear combination of a small set of structures. Pauling's theory is shown to be quite appropriate for describing anionic systems. specially the small ones, where the loosely bounded electron largely influences the properties of the systems. We verify the preference of some clusters for linear geometries.