Coupled cluster evaluation of the second and third harmonic scattering responses of small molecules

Abstract

The static and dynamic second harmonic (\(\beta _{\mathrm{SHS}}\)) and third harmonic (\(\gamma _{\mathrm{THS}}\)) scattering hyperpolarizabilities and depolarization ratios of water, carbon tetrachloride, chloroform, dichloromethane, chloromethane, and acetonitrile have been evaluated at the coupled cluster response theory level of approximation. Following two recent publications on their measurements, this is the first quantum chemical investigation on \(\gamma _{\mathrm{THS}}\) and on its decomposition into its spherical tensor components. Substantial electron correlation and basis set effects are evidenced for \(\beta _{\mathrm{SHS}}\) and \(\gamma _{\mathrm{THS}}\) and for their depolarization ratios, and they depend on the nature of the molecule. Then, using the selected CCSD/d-aug-cc-pVDZ level, the chlorinated methane derivatives have been studied, showing that (i) the \(\gamma _{\mathrm{THS}}\) response is dominated by its isotropic contribution, whereas (ii) for \(\beta _{\mathrm{SHS}}\) the dipolar contribution increases from carbon tetrachloride to dichloromethane, chloroform, chloromethane, and acetonitrile. Comparisons with the experimental data obtained from measurements in liquid phase (i) show that the increase of \(\gamma _{\mathrm{THS}}\) with the number for chlorine atoms is well reproduced by the calculations and (ii) suggest that the solvation effects are smaller for \(\gamma _{\mathrm{THS}}\) than for \(\beta _{\mathrm{SHS}}\).