Effect of monovacancies on the relative stability of fcc and hcp hard-sphere crystals

The effect of monovacancies on the free energy difference of close-packed hard-sphere crystals was examined. The monovacancy free energy and concentration were obtained via Monte Carlo simulations with a biased insertion method interpreted in a grand-canonical formalism. The difference in the effect of the vacancies to the difference between the free energies of the defect-free crystalline phases was compared. It was observed that the relative stability of stress-free fcc and hcp crystals is not affected by the presence of monovacancies, and fcc remaines the more stable phase over all solid-phase densities.