Orbital free ab initio simulation of surface freezing in a dilute Ga-Tl alloy

Abstract

We have used the orbital-free ab initio molecular dynamics method to study the phenomenon of surface freezing in a liquid Ga-Tl alloy (nominal Tl concentration of 0.14). Several thermodynamic states are considered from a high temperature of 675 K to a low temperature of 350 K. At the higher temperature the Tl atoms segregate to the surface and form a liquid layer. Upon cooling the layer eventually crystallizes into a close-packed hexagonal solid layer. These results agree with experiments for a dilute liquid alloy of Tl in Ga, except for some overestimation of the surface freezing temperature. X-ray reflectivity data are also well reproduced. The wavelength of the oscillatory density profile coincides with that deduced from experiments and with that obtained in earlier computer simulation results. We also analyze the consequences of surface freezing on the structure of the liquid in contact with the solid layer, finding no influence whatsoever, as the structure basically coincides with the bulk liquid one.