Freezing parameters of soft spheres

The phase switch Monte Carlo method is employed to determine the freezing properties of particles interacting via an r-12 repulsive potential. We establish that at the equilibrium freezing point the face centred cubic (fcc) structure has a free energy that is lower than that of the metastable body centred cubic (bcc) structure by 0.0184(4)kBT per particle. Thus the bcc structure is not the stable solid phase at freezing despite being commonly observed in simulations that physically nucleate the solid from the fluid. For the equilibrium fluid-fcc transition point we report accurate estimates of the coexistence pressure and densities for systems of sizes N = 108, N = 256 and N = 500 particles.