Quantum Monte Carlo simulations of Arn–CO2 clusters

Abstract

Potential-energy functions for CO2–Arn clusters are constructed using the pairwise-additive approximation from the Ar–Ar potential of Aziz [J. Chem. Phys. 99, 4518 (1993)] and three different CO2–Ar potentials which have been reported recently. These are used to find minimum-energy structures and to carry out rigid-body diffusion Monte Carlo simulations of the ground vibrational state for CO2–Arn clusters with n up to 30, as well as the first excited state for n=1. From these results, the CO2 ν3 redshift is estimated. For all values of n, the Ar atoms tend to surround the CO2 molecule. A complete first solvation shell is first found for n=14, and the largest complete first solvation shell is found for n=17. Although the most recent semiempirical CO2–Ar potential function of Hutson et al. [J. Chem. Phys. 105, 9130 (1996)] gives more accurate predictions of spectroscopic properties for n=1 than the best available ab initio potential function [Marshall et al., J. Chem. Phys. 104, 6569 (1996)], both potential functions give quite similar predictions for structures and approximate CO2 ν3 redshifts for larger values of n.