Covalentlike electronic effects in metallic liquids using an orbital-freeab initiomethod

Abstract

The origin of the unusual shoulder on the large-$q$ side of the main peak of the structure factors of liquid Ga and liquid Si is studied using an orbital-free ab initio molecular dynamics approach. The shoulders are found to be related to pairs of atoms that come close, supporting the earlier observation for liquid Ga based on a high temperature simulation. Results for Ga at lower temperature, and for Si at several applied pressures also show the relationship of the shoulder to pairs of atoms. The electron density near typical pairs shows an accumulation of charge between the atoms which in earlier work was taken to be an indication of a covalent bond. The calculated orbital-free electronic densities show a somewhat larger charge accumulation between the atoms than the previous Kohn-Sham calculations. This result was not anticipated because the orbital-free approach had not previously been expected to describe valence bonding. However, electron density distributions for Si for atomic configurations at several pressures calculated with the orbital-free approach compare very favorably with the results of Kohn-Sham calculations for the same configurations. On the other hand, analysis of the temperature dependence of the population of pairs and of their time evolution does not support the proposal that the pairs are covalently bonded. Other factors that may also contribute to the appearance of the shoulder are discussed.