Modelling of dielectric properties of non-linear optic materials based on linear molecules

Abstract

Abstract Dependence of polarizability (LP) and hyperpolarizability (HP) of linear oligomers on the number of monomers in the chain is analyzed. A critical review of previous studies revealed two main issues. Firstly, the specific (per one chain unit) values of both LP and HP monotonously increase along with the chain length, and secondly, both dependencies approach the limit values in sufficiently long chains. A model describing such behavior is proposed. The model parameters are LP and HP of an isolated chain unit and a cross-term, which couples the dipole moments of neighboring units. These parameters have a clear physical meaning. It is shown that the theoretical predictions provided by the model agree well both with the results of accurate quantum-mechanical calculations and with experimental data.