First Principles Molecular Dynamics Studies of Liquid and Solid Sodium

Abstract

One of the outstanding problems in materials science is the lack of a fundamental theory of melting and freezing. Such a theory would be extremely useful in the search for new materials. For example, the high-temperature properties of alloys almost always limit the efficiency that can be achieved in an engine or power plant. Also the mechanical strength of materials is often determined by the distribution of impurities, which in turn is a result of the cooling (or annealing) that occurs during pro cessing. To address these problems we have used the technique of molecular dynamics simulation in which 50 to 100 atoms are followed on the computer as they move. From these simulations it is possible to calculate the important thermal properties such as the rate of dif fusion, the internal energy, the free energy, and the volume of the material above and below the melting temperature. These calculations make use of a new theory that combines molecular dynamics simulation with calculations of the electron states and therefore re quires no adjustable parameters as inputs.