Molecular-based virial coefficients of CO₂-H₂O mixtures

We report second and third virial coefficients for the system CO₂-H₂O, calculated via cluster integrals using quantitative molecular models taken from the literature. Considered models include (1) fits to highly accurate ab initio calculations of the potential energy surfaces, and (2) semiempirical Gaussian Charge Polarizable Models (GCPM). Three-body effects are found to be essential for obtaining quantitative results. Good agreement with experiment is obtained for the pure-component coefficients, and for the cross second virial coefficient. For the two cross third virial coefficients, the few experimental data available do not agree well with the calculations; it is not clear whether this is due to problems with the data or deficiencies in the three-body potentials. The uncertain state of the experimental data, and the relative mutual consistency of values computed from ab initio and GCPM models, suggest that calculated mixture third virial coefficients could be more accurate than values from experiment.