Liquid Bi–Pb and Bi–Li alloys: Mining thermodynamic properties from ab-initio molecular dynamics calculations using thermodynamic models

Abstract

Ab-initio molecular dynamics (AIMD) simulations, coupled with thermodynamic models, can be used to extract thermodynamic properties such as mixing enthalpies, activities and free energies in the liquid state, even when the published AIMD data provide no direct access to such information. In order to demonstrate this fact, in the present work we used AIMD structural data from the literature on molten Bi–Pb and Bi–Li alloys as raw material for describing thermodynamic properties. The analytical description is divided in two parts. In the first part, we employ the Bethe-Peierls (quasi-chemical) approximation in the disordered state to describe the thermodynamics of Bi–Pb molten alloys, since it is verified experimentally that this binary liquid is practically a regular solution. The agreement with experimental activity and mixing enthalpy measurements from the literature is excellent. Conversely, the same approach cannot be applied to liquid Bi–Li alloys, in which the presence of transient clusters with composition around 75 at% Li prevents the use of the Bethe-Peierls model. Therefore, in the second part of the work, we used the original and a modified version of the Quasi-Lattice model to successfully describe the AIMD data and accordingly write the thermodynamic properties of liquid Bi–Li alloys. Also in this case, it is seen that a good agreement was reached between the results derived from AIMD calculations and experimental thermodynamic measurements from the literature. We conclude that AIMD calculations for liquid melts, although computationally expensive, can be very accurate, and therefore could be applied in thermodynamic descriptions, with an appropriate thermodynamic model, even when the original AIMD calculations were not explicitly concerned with thermochemical data.