Investigating the first hyperpolarizability of liquid carbon tetrachloride

Sequential QMMM calculations have been carried out to investigate the first hyperpolarizability (β _HRS,Liq) of liquid CCl₄. First, Monte Carlo simulations are performed to generate statistically uncorrelated snapshots representing the liquid structure. Then, the first hyperpolarizability of selected snapshots are evaluated using ab initio calculations. In these calculations the solvent effects are described either exclusively by point charges or a few neighboring CCl₄ molecules are also explicitly considered. In particular, it has been observed that considering small numbers of CCl₄ molecules, embedded in point charges, enables monitoring the emergence of the dipolar contribution to β_HRS,Liq and the increase of the depolarization ratio, confirming experimental results and substantiating that the dipolar contributions originate from intermolecular interactions between the CCl₄ molecules. Additional calculations using semi-empirical Hamiltonians for the QM part were performed on systems containing explicitly one or two solvation shells, and further confirmed the emergence of the dipolar contribution in liquid CCl₄.