Computational study of the melting-freezing transition in the quantum hard-sphere system for intermediate densities. I. Thermodynamic results.

The points where the fluid-solid (face-centered-cubic) transition takes place in the quantum hard-sphere system, for reduced densities 0.85>rhoN*>0.5 (reduced de Broglie wavelengths lambdaB*<or=0.8), have been determined via calculations of Helmholtz free energies. A number of complementary methods have been utilized, namely, path-integral Monte Carlo simulations for fixing the basic thermodynamic and structural quantities, Ornstein-Zernike computations of the fluid isothermal compressibilities using the centroid correlations, and applications of the Einstein crystal technique. Attention is paid to the evaluation of the statistical uncertainties in the isothermal compressibilities and also to the quantum implementation of the Einstein crystal technique by including explicitly the constraint of fixed center of mass. The equation of state along the fluid lambdaB* branches studied has been determined with two methods, one based on the isothermal compressibilities and the other on the usual virial estimator. Along the solid lambdaB* branches the equation of state has been fixed with the virial estimator. The results indicate that the phase transition investigated is governed by entropic effects and that the fluid-solid coexistence densities are arranged along a straight line rhoFCC*=rho(rhoF*), a behavior which at least holds even for lambdaB*<2, as revealed by completing the present analysis with data available in the literature.