Relating melting trends and elasticity in simple metals: an empirical potential approach

TL;DR

This paper develops analytic interatomic potentials for alkali metals to accurately predict melting points and thermodynamic properties from static crystalline data, showing high transferability and agreement with experiments.

Contribution

It introduces a new set of empirical potentials fitted to static properties that can reliably predict melting points and phase stability without finite temperature data.

Findings

Good agreement with experimental melting points (except Li)

Reproduction of bcc instability in Li and Na at low temperatures

Potentials are highly transferable and broadly useful for alkali metals

Abstract

We demonstrate that the melting points and other thermodynamic quantities of the alkali metals can be calculated based on static crystalline properties. To do this we derive analytic interatomic potentials for the alkali metals fitted precisely to cohesive and vacancy energies, elastic moduli, lattice parameter and crystal stability. These potentials are then used to calculate melting points by simulating the equilibration of solid and liquid samples in thermal contact at ambient pressure. With the exception of lithium, remarkably good agreement is found with experimental values. The instability of the bcc structure in Li and Na at low temperatures is also reproduced, and, unusually, is not due to a soft T1N phonon mode. No forces or finite temperature properties are included in the fit, so this demonstrates a surprisingly high level of intrinsic transferrability in the simple potentials. Currently, there are few potentials available for the alkali metals, so in, addition to demonstrating trends in behaviour, we expect that the potentials will be of broad general use.