A New Set of Combining Rules for Mie (λ, 6) Potential

Force fields based on the Mie (λ, 6) potential, combined with theoretical methods and molecular simulations, offer a promising framework for predicting the thermophysical properties of fluids. Despite this potential, the availability of reliable combining rules for unlike interaction parameters in mixtures remains limited, thereby constraining the broader application of Mie (λ, 6)-based force fields. In this study, a new set of combining rules for the Mie (λ, 6) potential is proposed, derived by using a distortion model for the repulsive interaction and a geometric mean approximation for the attractive interaction, combined with first-order mathematical approximations. The capability of the new combining rules was first evaluated for noble gas pairs modeled with the Lennard-Jones potential, a specific case of Mie (λ, 6) potential with λ = 12, for which experimentally derived data on unlike interaction parameters are available. The results showed noticeably better agreement with experimentally derived values than those obtained using the two commonly used combining rules. Further assessment was carried out through the evaluation of Henry's law constants, phase diagrams, and excess molar volumes, which are highly sensitive to cross-interactions, for various binary mixtures modeled using the Mie chain coarse-grained force field, obtained from NVT-GEMC, NPT-GEMC, and NPT-MC simulations, respectively. For mixtures with similar Mie (λ, 6) potential parameters for the components, all of the combining rules, including the new ones, yielded comparable predictions. In contrast, for asymmetric systems with significant force field parameter disparities, the new rules yielded substantially improved accuracy relative to experimental data for all considered thermodynamic properties, whereas the commonly used combining rules exhibited poor performance with markedly larger deviations. These findings highlight the improved robustness and broader applicability of the proposed combining rules for extending Mie (λ, 6)-based force fields to complex fluid mixtures.