Modified 2CLJDQP model and the second virial coefficients for linear molecules

A modified form of 2CLJDQP potential model is proposed to calculate the second virial coefficients of two-center Lennard-Jones molecules. In the presented potential model, the potential parameters σ and ε are considered as the temperature-dependent parameters in the form of hyperbolical temperature function based on the theory of temperature-dependent potential parameters. With this modified model, the second virial coefficients of some homonuclear molecules (such as O₂, Cl₂, CH₃CH₃, and CF₃CF₃) and heteronuclear molecules (such as CO, NO, CH₃F, CH₃Cl, CH₃CF₃, CH₃CHF₂, and CF₃CH₂F) are calculated. Then the Lorentz–Berthelot mixing rule is modified with a temperature-dependent expression, and the second virial coefficients of the heteronuclear molecules (such as CH₃F, CH₃Cl, and CH₃CF₃) are calculated. Moreover, CO₂ and N₂O are also studied with the modified 3CLJDQP model. The calculated results from the modified 2CLJDQP model accord better with the experimental data than those from the original model. It is shown that the presented model improves the positive deviation in low temperature range and negative deviation in high temperature range. So the modified 2CLJDQP potential model with the temperature-dependent parameters can be employed satisfactorily in large temperature range.