Adsorption equilibria in an isobaric ensemble

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Abstract
We present the results of an investigation of adsorption equilibria at fluid/solid interfaces using Monte Carlo simulations in an isobaric-isothermal ensemble. The method permits the study of adsorption equilibrium at fixed values of the bulk fluid pressure and is equally useful for bulk states varying from the dilute gas to the dense liquid. The method is applied first to hard sphere/hard wall systems in one and three dimensions. In one dimension the results are compared with the exact analytical results for the density profile. The method is also applied to a Lennard-Jones 12-6/9-3 model of an argon/graphite interface. In this case results for adsorption from the subcritical vapor are compared with those from grand ensemble Monte Carlo simulations. Generally good agreement is found between the two methods. However, the adsorption excess at multilayer conditions can be obtained with significantly greater precision via the isobaric method for a given investment of computer time.