A b i n i t i o studies of structural features not easily amenable to experiment. II. The influence of bond delocalization effects on the molecular structures of some lithium fluoride clusters

Abstract

The geometries of linear and cyclic forms of Li₂F₂ and Li₃F₃ were determined by unconstrained ab initio force relaxations using the 4‐31G basis set on F and 5‐21G on Li. Optimized Li–F bond distances depend strongly on their molecular environment. Linear clusters are more stable than bent chains. Planar, cyclic forms are more stable than open chains. Some of the refined structures deviate significantly from the equilibrium geometries calculated for these molecules on the basis of electrostatic bonding models. It is concluded that the ionic bonding concept may be intrinsically deficient in quantitatively rationalizing the molecular structures even of systems the potential energy minima of which are primarily determined by electrostatic interactions.