Ab initio simulations of non-stoichiometric lithium-oxygen clusters

Bonding and electronic properties of non-stoichiometric lithium oxide clusters LinO2 (n less than or equal to 10) are studied by means of ab initio simulations. We focus on the first stage of lithium enrichment of stoichiometric Li4O2, where the formation of additional Li-O bonds is favoured. The bonding configuration of the lowest-energy isomers and their stability are analysed in detail, and their structures compared to those found in bulk non-stoichiometric alkali-metal suboxides. As a function of the increasing number of excess Li atoms, coexistence of an ionic and a delocalized character of the electronic density takes place, accompanied by a progressive Li-O bond weakening. These issues, and the existence of odd-even staggering of electronic properties, are discussed, in relation to recent experiments and other anion-deficient systems such as defective oxide surfaces and alkali-metal halide clusters.