Large basis set ab initio calculations of the dipole polarizabilities and second hyperpolarizabilities of a large set of organic molecules have been carried out and the results have been used to assess additivity and transferability of atomic contributions to the overall molecular response tensors. Reasonable estimates of the mean second hyperpolarizability response can be obtained from summing atomic parameters obtained here, though the reliability of the estimates is worse than what is found for dipole polarizabilities. Individual tensor elements are not as well determined from transferable, additive contributions, which means that the orientational nature of the response is more subject to local bonding features.

Nonlinear optical (NLO) properties of transition metal complexes are studied using quantum chemical calculations. By comparison with all electron calculations, effective core potentials have been shown to be competent for the calculation of NLO properties as long as the valence basis sets are comparable. While overall the basis set effects are important for calculation of NLO properties, they are found to be less important for the central transition metal than for the surrounding ligands. Augmenting the basis set of main group elements with diffuse s, p, and d functions in a proper way could provide the best compromise between speed and accuracy of the computation. Interesting trends are found in the calculation of NLO properties of [MO 4 ] q-. Both polarizability (R) and second hyperpolarizability (γ) decrease toward the right across the transition series. The second series [MO 4 ] q-have the largest R among the three metalates in a triad. For group IVB and VB complexes with larger charges (-4 and -3, respectively), the second series [MO 4 ] qhave the largest γ, while for groups VIB, VIIB, and VIII, with less anionic metalates (-2, -1, and 0, respectively), the third series metalates have the largest γ. The relative difference in both R and γ values among the three series in the same group is much smaller than between different groups. Overall, variations in the calculated values of NLO properties correlate with M-O bond lengths and hence the size of the metalate ion.

A systematic study of nonlinear optical (NLO) properties of inorganic transition metal (TM) thiometalates and metalates is reported. Polarizabilities (R) and second hyperpolarizabilities (γ) are calculated in solution within the polarizable continuum model. It is found that NLO properties of anionic inorganic complexes can be successfully modeled in solution, when this cannot be done so in the gas phase. Solvent effects are found to significantly increase R and γ. The effects are stronger on γ (up to 80%) than on R (up to 40%) and stronger on TM thiometalates than on metalates. For R, solvent effects are found to be more important than electron correlation effects. For γ, the two effects are similarly important. Solvent effects on R and γ caused by subordinate factors other than the dominant electrostatic solute-solvent interactions were studied and assessed to be negligible. Upon solvation, large TM and ligand modification effects on R and γ are found. One oxo-to-sulfido substitution results in an increase in R by 38 au and γ by 10 000 au.

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An initial effort to study the nonlinear optical (NLO) properties of interacting transition-metal-oxo complexes is presented and studied by effective core potential approaches. Osmium tetroxide is used for this study. Favorable intermolecular interaction effects, even within this weak interaction regime, that yield enhancements in NLO properties have been found. Interaction effects increase alpha (polarizability) up to 6% and gamma (second hyperpolarizability) up to 100% relative to the isolated monomer result for OsO4. The magnitude of the interaction (hyper)polarizabilities, and indeed even the sign, is found to be quite sensitive to the relative orientation of the osmium tetroxide monomers.