Monte Carlo Simulations of the Effect of Cross-potential Variations on the Equation of State of N$_2$/CO$_2$ Mixtures and of Detonation Products

The issues of mixing and cross-potentials were studied with particular emphasis on the implications for detonation products equation of state (EOS) and the prediction of measurable sensitivity to the cross-potential. A large number of Monte Carlo simulations were made with the choice of ensemble depending on the system being studied: NPT for uniform mixing, Gibbs for fluid-fluid phase separation, and Composite for full detonation products with chemical equilibrium and carbon clusters. Simulations with N$_2$/CO$_2$ mixtures demonstrate significant sensitivity to the cross-potential in the EOS values for uniform mixtures, in the shape of the isotherms and the location of rapid changes due to fluid-fluid phase separation, and in the location of the fluid-fluid phase separation line in pressure and temperature. Suggestions are made for experimental methods to characterize the cross-potential and mixing properties. Evaluation of the full EOS for HMX based explosives demonstrates an amplified effect of the cross-potential variation through dramatic shifts in thermodynamic equilibrium composition and the resulting EOS.