REFINEMENT OF NONBONDING INTERACTION PARAMETERS FOR CARBON-DIOXIDE ONTHE BASIS OF THE PAIR POTENTIALS OBTAINED BY MP2 6-311+G(2DF)-LEVEL AB-INITIO MOLECULAR-ORBITAL CALCULATIONS/

The nonbonding interaction energies of carbon dioxide dimer were calcu lated using several basis sets to evaluate the basis set effects. Larg e basis sets including multiple polarized functions were necessary to evaluate the interaction energies correctly. Small basis sets consider ably underestimated the interaction energies. Nonbonding parameters of a model potential of carbon dioxide were refined based on the intermo lecular interaction energies of 40 geometrical configurations of dimer s calculated by an MP2/6-311+G(2df)-level ab initio method with the ba sis set superposition error (BSSE) correction. The molar volume and he at of evaporation of liquid carbon dioxide obtained from molecular dyn amics simulations with the model potential reproduced the experimental values with an error of only a few percent. On the other hand, the mo del potential based on the BSSE-uncorrected interaction energies overe stimated the attractive interaction and failed to reproduce the experi mental values. The structure and lattice vibrational frequencies of ca rbon dioxide molecular crystal in the low-pressure phase (1 atm) and t he structure in the high-pressure phase (20 GPa) were also well reprod uced by the same model potential proposed here.