Ab initioWannier-function-based correlated calculations of Born effective charges of crystallineLi2Oand LiCl

Abstract

In this paper, we have used our recently developed ab initio Wannier-function-based methodology to perform extensive Hartree-Fock and correlated calculations on ${\mathrm{Li}}_{2}\mathrm{O}$ and LiCl to compute their Born effective charges. Results thus obtained are in very good agreement with the experiments. In particular, for the case of ${\mathrm{Li}}_{2}\mathrm{O}$, we resolve a controversy originating in the experiment of Osaka and Shindo [Solid State Commun. 51, 421 (1984)] who had predicted the effective charge of Li ions to be in the range of 0.58--0.61, a value much smaller compared to its nominal value of unity, thereby, suggesting that the bonding in the material could be partially covalent. We demonstrate that effective charge computed by Osaka and Shindo is the Szigeti charge, and once the Born charge is computed, it is in excellent agreement with our computed value. Mulliken population analysis of ${\mathrm{Li}}_{2}\mathrm{O}$ also confirms ionic nature of the bonding in the substance.