Calculation of thermodynamic properties of vapor–liquid equilibria using ab initio intermolecular potential energy surfaces for dimer O2–O2

The two 5-site potentials from ab initio calculations at the theoretical level CCSD(T) with correlation consistent basis sets aug-cc-pVmZ (with m = 4, 34) have been constructed from oxygen. The extrapolation ab initio energies were approximated by the basis sets aug-cc-pVmZ (m = 3, 4). These two potentials were constructed by using the ab initio intermolecular energy values and a non-linear least-squares fitting method. The second virial coefficients of oxygen were determined to demonstrate the accuracy of these ab initio 5-site potentials. These ab initio potentials were employed to estimate the thermodynamic properties of the vapor���liquid equilibria by GEMC simulation. The influence of ab initio potential alone and plus 3-body interaction Axilrod-Teller potential was investigated within GEMC simulation from 80 K to 140 K. The discrepancy between them is insignificant. This showed that the two 2-body 5-site potential functions can also be used together with the 3-body interaction Axilrod-Teller potential to generate the accurate thermodynamic properties of the liquid���vapor equilibria.