Molecular Dynamics Calculations for Sodium using Pseudopotential Theory

We study the equation of state of sodium using the molecular dynamics technique whereby the classical motion of a system of ions is solved with the aid of computers. The interaction potential between pairs of sodium ions consists of coulomb and Born-Mayer repulsion terms and an effective ion-ion interaction derived from pseudopotential theory. This theory includes the effects of electron gas screening, exchange, and correlation. We use a model pseudopotential with parameters fit to experimental low-temperature data. By using this technique, we are able to begin with an atomic description of a simple metal and proceed to calculate its macroscopic thermodynamic properties. We calculate equation-of-state points consisting of the total internal energy in volume and temperature space. We illustrate the unique capabilities of the molecular dynamics technique by inducing a dynamic bcc-to-hcp martensitic phase change. The results of this study demonstrate that the molecular dynamics technique, coupled with an interaction potential that adequately describes the ion-ion interaction in a simple metal, can be used to calculate the macroscopic properties of such systems.