Computational Study of Materials Under Pressure

Book excerpt: "Pressure possesses perhaps the greatest of all the physical variables. First principles electronic structure calculations have contributed significantly to high perssure studies, especially of solids. In this work, the results of the first principles analysis of CoN, MnO and Li under pressure are presented. From total energy calculations, we can establish that CoN takes a paramagnetic zincblende structure at ambient pressure, rather than rocksalt as sometimes suggested. We also predict a first order phase transition to a ferromagnetic state at 43 GPa, a weak ferromagnet not far from a ferromagnetic quantum critical point. MnO, a classic prototype for a Mott insulator exibits rich physics as a function of pressure, including structural phase transition, volume collapse, insulator - metal transition, etc. This system has been a long standing challenge to methods based on density functional theory. Our study provides some of the first detailed information on how magnetic moments in a real material may begin to disintegrate without vanishing identically, at or near a Mott transition, when correlation is taken into account. Li, the simplest metal becomes a superconductor under pressure, with the highest Tc observed in any elemental metal. Using both total energy and linear response calculations we observe increasingly strong electron-phonon coupling concentrated along intersections of Kohn anomaly surfaces with the evolving Fermi surface, that drives this simple metal to become a superconductor under pressure"--