Identifying and evaluating organic nonlinear optical materials via molecular moments

We demonstrate how to appropriately estimate the zero-frequency (static) hyperpolarizability of an organic molecule from its charge distribution, and we explore applications of these estimates for identifying and evaluating new organic nonlinear optical (NLO) materials. First, we calculate hyperpolarizabilities from Hartree-Fock-derived charge distributions and find order-of-magnitude agreement with experimental values. We show that these simple arithmetic calculations will enable systematic searches for new organic NLO molecules. Second, we derive hyperpolarizabilities from crystallographic data using a multipolar charge-density analysis and find good agreement with empirical calculations. This demonstrates an experimental determination of the full static hyperpolarizability tensor in a solid-state sample.