Accurate simulation estimates of phase behavior in ternary mixtures with prescribed composition

This paper describes an isobaric semi-grand canonical ensemble Monte Carlo scheme for the accurate study of phase behavior in ternary fluid mixtures under the experimentally relevant conditions of prescribed pressure, temperature and overall composition. It is shown how to tune the relative chemical potentials of the individual components to target some requisite overall composition and how, in regions of phase coexistence, to extract accurate estimates for the compositions and phase fractions of individual coexisting phases. These estimates have finite-size errors that are exponentially small in the system size even when the phase fraction of one phase is vanishingly small, as occurs at the coexistence boundary. The method is illustrated by tracking a path through the composition space of a model ternary Lennard-Jones mixture.