Displacive Phase Transformations and Phonons

Abstract

The use of first principles calculations to help understand materials properties has gone from wishful thinking, to feasible, to invaluable, largely because of the doubling of computing power every 18 months for the last 30 years,. We are still, however, just beginning the era when such calculations will become a factor in the synthesis, processing, and development of materials by design. Other papers in these proceedings demonstrate the utility of modern electronic structure calculations, particularly in arriving at the low temperature ground state configurations and energies. In this paper we focus on the use of such calculations to determine the stability of a material or compound of fixed stoichiometry as a function of temperature or pressure. Our emphasis will be on displacive structural phase transformations from one crystal symmetry to another. The goal of the studies reviewed is to identify and understand the details of the microscopic electronic interactions responsible for the transformations. In this manuscript we illustrate by way of a few prototypical examples the kind of information attainable with modern computational resources. The materials to be considered include Ba, Na, and the intermetallic compounds NiTi and NiAl. We conclude with some speculation on how massively parallel computers will soon enhance the theoretical landscape.