Simulations of phase equilibria in planar slits

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Abstract
Gas-liquid coexistence, free energies and surface forces are investigated for a simple fluid confined by planar walls, which also interact with the fluid. Isotension ensemble simulations and an infinite order thermodynamic perturbation theory are utilized. The free energies are calculated to high accuracy as a function of the separation between the walls. At a particular separation the fluid undergoes a phase transition and both gas and liquid branches are simulated. A new ensemble, the restricted isotension ensemble, is introduced: this prevents interphase crossings between gas and liquid phases, near the critical temperature. This ensemble may prove useful for further studies of wetting phenomena.