Modeling nonlinear optical properties of inorganic complexes. Counterion effects Original Research Article

Counterion effects on nonlinear optical (NLO) properties of transition metal metalates are studied using a supermolecule approach by surrounding [MO4]q− with alkali metal cations (A+)4 (A=Li, Na, K). Computational results show that counterion interaction effects on the NLO properties are large and highly dependent on the separation distances between the counterions and the central transition metal. At shorter separation distances, which are experimentally relevant, ligation of alkali metal counterions decreases the NLO properties of the whole system. This results in attenuation of the predicted NLO properties of the complexes vs. the sum of the constituent properties. Lengthening this separation distance would enhance the nonlinearity of the system. Trends in counterion interactions as function of alkali metal cations and central transition metals have been studied and employed to predict the magnitude of nonlinearity. The effect of the basis set superposition error (BSSE) and the corresponding counterpoise correction are found to be small for the property calculations.