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.

Structure of free surface crystallization of Hg: a first attempt

“…The first peak is always lower than the second one. At T = 235K, the density in the central region is equal to 13.7 g/cm 3 , in excellent agreement with the measured bulk density of l-Hg at this temperature. The oscillations penetrate four atomic diameters into the bulk region.…”

“…This is a long standing problem whose goal is to understand how surface induced-layering depends on the interactions between atoms [3]. It had long been believed that layering was absent at the liquid surface of simple fluids with isotropic interactions, and consequently thought to be unique to metallic liquids, many of them being characterized by a high critical temperature T C and a low melting temperature T M .…”

Structural, dynamic, and electronic properties of liquid tin: An ab initio molecular dynamics study

“…The maximum of g͑r͒ occurs at a somewhat smaller distance than at 573 K, around 3.02 Å, and the distance of closest approach also diminishes to 2.41 Å. This feature, also shared by liquid Ga, 30 suggests a rather soft repulsive interaction, that enables a closer approach when a higher kinetic energy is available.…”

“…30 In order to check if it also holds for l-Sn we have computed the static structure factor, S͑q , r b ͒, corresponding to only those atoms that have a neighbor closer than a distance r b , analyzing its variations as r b changes within the range spanned by the distribution function of the distance to the first neighbor of a given atom. Notice that for larger values of r b , we have S͑q , r b ͒ = S͑q͒.…”

Cluster melting: new, limiting, and liminal phenomena

“…The structure of bulk liquid gallium is rather anomalous, as liquid metals go [87][88][89] but contains no strong pointers to the origin of this phenomenon. However, if the surface bonding between gallium atoms, in this size range where the standard phase is strongly disfavoured, becomes competitive with the bonding experienced by an atom at the centre of the cluster, then we are perhaps in a liminal regime where interesting things start to happen.…”