The Ab Initio Treatment of High-Pressure and High-Temperature Mineral Properties and Behavior

Abstract

Ab initio techniques, mainly based on the implementation of quantum mechanics known as density functional theory (DFT), have now become widely used in the investigation of the high-pressure and high-temperature properties of materials. These techniques have been proven reliable and accurate and as such can be considered in many cases as complementary to experiments. Here, I will describe some of the ab initio techniques that have been used in the past to study the properties of the constituents of the Earth's interior. I will start the discussion by briefly summarizing the main ideas of DFT, and then, I will describe the applications of this technique to the evaluation of a number of static and dynamic properties of the Earth's forming minerals. Low-temperature properties of solids have often been studied using the quasi-harmonic approximation, which sometimes can retain high accuracy even at temperatures not too far from the melting temperature. After a brief introduction of the techniques, some examples of these quasi-harmonic theory-based studies will be provided. For solids at high temperature and for liquids, the quasi-harmonic approximation fails, and I will describe how using the molecular dynamics technique, coupled with ab initio calculations and the thermodynamic integration scheme, it is possible to compute the high-temperature thermodynamic properties of both solids and liquids. Examples of the application of these techniques will include the calculation of melting curves, the transport properties, and the thermodynamics of solutions and how these calculations have been used to improve our understanding of the Earth's core.