Free energies, vacancy concentrations and density distribution anisotropies in hard--sphere crystals: A combined density functional and simulation study

TL;DR

This study compares free energies and density distributions in hard sphere crystals using Monte Carlo simulations and density functional theory, finding good agreement and highlighting the effectiveness of Fundamental Measure functionals.

Contribution

It demonstrates the accuracy of Fundamental Measure theory in predicting free energies and density distributions in hard sphere crystals, including vacancy concentrations.

Findings

Good agreement between FMT and simulations for free energies

Fundamental Measure theory predicts narrower density peaks with more anisotropy

White Bear II functional provides physically sensible vacancy concentrations

Abstract

We perform a comparative study of the free energies and the density distributions in hard sphere crystals using Monte Carlo simulations and density functional theory (employing Fundamental Measure functionals). Using a recently introduced technique (Schilling and Schmid, J. Chem. Phys 131, 231102 (2009)) we obtain crystal free energies to a high precision. The free energies from Fundamental Measure theory are in good agreement with the simulation results and demonstrate the applicability of these functionals to the treatment of other problems involving crystallization. The agreement between FMT and simulations on the level of the free energies is also reflected in the density distributions around single lattice sites. Overall, the peak widths and anisotropy signs for different lattice directions agree, however, it is found that Fundamental Measure theory gives slightly narrower peaks with more anisotropy than seen in the simulations. Among the three types of Fundamental Measure functionals studied, only the White Bear II functional (Hansen-Goos and Roth, J. Phys.: Condens. Matter 18, 8413 (2006)) exhibits sensible results for the equilibrium vacancy concentration and a physical behavior of the chemical potential in crystals constrained by a fixed vacancy concentration.