Liquid-vapour asymmetry in pure fluids: a Monte Carlo simulation study

Monte Carlo simulations within the grand canonical ensemble are used to obtain the joint distribution of density and energy fluctuations pL(ρ, u) for two model fluids: a decorated lattice gas and a polymer system. In the near critical region the form of pL(ρ, u) is analysed using a mixed field finite-size-scaling theory that takes account of liquidvapour asymmetry. Field mixing transformations are performed that map pL(ρ, u) onto the joint distribution of critical scaling operators p̃⋆(x, y) appropriate to the Ising fixed point. Carrying out this procedure permits a very accurate determination of the critical point parameters. By forming various projections of p̃⋆(x, y), the full universal finite-size spectrum of the critical density and energy distributions of fluids is also obtained. In the sub-critical coexistence region, an examination is made of the influence of field mixing on the asymmetry of the density distribution. PACS numbers 64.70F, 05.70.Jk