CALCULATION OF VIRIAL COEFFICIENTS AND VAPOR PRESSURE OF SYSTEM CO-CO USING AB INITIO QUANTUM CALCULATION

Abstract

The 5-site ab initio intermolecular potential of the CO-CO system was developed from quantum chemical calculations at the theoretical CCSD (T) level with the correlation basis set aug-cc-pVQZ. The 5-site ab initio pair potential developed here is based on the Morse potential. The optimum coefficients of the ab initio pair potential of the CO-CO sys-tem are determined by combining the differential evolution algorithm and the Levenberg-Marquardt algorithm. The 5-site intermolecular potential ab initio is used to determine the second virial coefficients of the CO-CO system by the four-dimensional integration method. The calculated second virial coefficients of the CO-CO system fit well with the experimental data. In addition, ab initio calculation CCSD(T) / aug-cc-pVQZ is also combined with the COSMO method to calculate the screening charge density of the molecule CO to determine the physicochemical properties such as vapor pressure and the critical pressure of the liquid CO. The results obtained show that the difference between the theoretical calculations in this work versus the experiment is insignificant.