Numerical Simulation of Coulombic Freezing

Abstract

The fluid to crystalline solid first order phase transition of the classical one component plasma (OCP) has been studied by Monte Carlo simulation in three dimensions for temperatures below the thermodynamic freezing temperature (Γ = Z²e²/akT = 180, a = Wigner-Zeitz radius). With N = 686 we found freezing from a metastable supercooled fluid into microcrystals for values of Γ ranging from 250 to 700. In one case, Γ = 500, the system froze into a perfect bcc lattice from a random start. With more particles the system froze into two or more crystals one bcc and one fcc and smaller examples of hcp. The lattice planes were examined and various kinds of crystal defects could be observed. We developed a program for determining the local environment of each particle as bcc, fcc, hcp, or fluid in order to identify microcrystals in the system at any stage of the freezing process. Generally freezing proceeds rapidly when any single miciutrystal attains a sufficient size or roughly 60 to 70 particles. The observations of freezing seem to agree with classical nucleation theory. No separate glass phase (non-crystalline) was seen.