Ab initio intermolecular potential energy surface for the CO₂-N₂ system and related thermophysical properties

A four-dimensional potential energy surface (PES) for the interaction between a rigid carbon dioxide molecule and a rigid nitrogen molecule was constructed based on quantum-chemical ab initio calculations up to the coupled-cluster level with single, double, and perturbative triple excitations. Interaction energies for a total of 1893 points on the PES were calculated using the counterpoise-corrected supermolecular approach and basis sets of up to quintuple-zeta quality with bond functions. The interaction energies were extrapolated to the complete basis set limit, and an analytical site-site potential function with seven sites for carbon dioxide and five sites for nitrogen was fitted to the interaction energies. The CO₂-N₂ cross second virial coefficient as well as the dilute gas shear viscosity, thermal conductivity, and binary diffusion coefficient of CO₂-N₂ mixtures were calculated for temperatures up to 2000 K to validate the PES and to provide reliable reference values for these important properties. The calculated values are in very good agreement with the best experimental data.