Solution of reference interaction site model for mixtures of short-chain polyatomic molecules

Mixtures of chain molecules—monomers, dimers, trimers, and tetramers—are studied using the soft interaction site model. The site–site Ornstein–Zernike equations are solved using the Percus–Yevick closure. The site–site potential is of the Lennard-Jones 12-6 type. The method of solution, based on the efficient algorithm of Labik and employing Newton–Raphson accelerations, is shown to be fast, accurate and stable; it also shows good convergence behavior even with inaccurate initial estimates. New symmetrical properties among the atom–atom pairs are used to simplify the Jacobian matrix of solution. Pure as well as mixture systems are investigated. Comparison with simulation data of Bañon et al. and Massobrio et al. is made. The structure is qualitatively described by the integral equations. The internal energy is well predicted by the reference interaction site model calculations.