Decomposing molecular nonlinear optical properties

Abstract

Great attention has been paid to materials that are characterized by a large nonlinear optical response, as they being commonly used in new technologies such as optical communication technology, optical rectification. The nonlinear optical properties of the materials strongly depend on the intermolecular interactions. For that reason, the understanding of different intermolecular interactions on nonlinear optical properties is so important, since it can allow a better knowledge of these properties and so, facilitate the design of new types of materials with large NLOP. In this work, it is investigated the role of the different contributions to the NLOP of a set of dimers, all of them with a HCN molecule as a monomer. Whereas for the dipole moment and polarizability of the studied dimers the main contribution is the electronic, the nonlinear optical properties (first and second hyperpolarizability) are governed by vibrational contribution. The NLOP properties will be partitioned in two different ways, all based on methodologies used to decompose the molecular energy. The first one, is a variational-perturbational energy decomposition scheme (VP-EDS), which split the NLOP into different interaction energy contributions like electrostatic or repulsion exchange. The second one is a real-space partition of the NLOP that splits the property in to an origin-independent atomic contributions. The decompositions with VP-EDS have shown, in general, some tendency on its terms (i.e. always increase or always decrease while increasing the atomic number of the atom bonded to the halogen). The comparison with other kind of interactions, such as hydrogen bonds, showed that the tendencies are quite similar between the two types of interactions. For instance, for Δμel the predominant term is electrostatic and the second one is delocalization, decreasing while increasing the volume of the atom(s) bonded to the halogen/hydrogen. Unexpectedly, the real space origin-independent methodology showed that, instead of distributing the excess of the property due to the interaction into the two monomers, all excess property is concentrated in the HCN monomer