A Multi‐Scale Approach to Simulate the Nonlinear Optical Response of Molecular Nanomaterials

Nonlinear optics is essential for many recent photonic technologies. Here, we introduce a novel multi-scale approach to simulate the nonlinear op-tical response of molecular nanomaterials combiningab initioquantum-chemical and classical Maxwell-scattering computations. In this approach,the first hyperpolarizability tensor is computed with time-dependent density-functional theory and incorporated into a multi-scattering formalism thatconsiders the optical interaction between neighboring molecules. Such incorporation is achieved by a novel object: the Hyper-Transition(T)-matrix.With this object at hand, the nonlinear optical response from single molecules and also from entire photonic devices can be computed, including thefull tensorial and dispersive nature of the optical response of the molecules, as well as the optical interaction between different molecules as, for ex-ample, in the lattice of a molecular crystal. To demonstrate the applicability of our novel approach, the generation of a second-harmonic signal froma thin film of an Urea molecular crystal is computed and compared to more traditional simulations. Furthermore, an optical cavity is designed, whichenhances the second-harmonic response of the molecular film up to more than two orders of magnitude. ... mehrOur approach is highly versatile and accurateand can be the working horse for the future exploration of nonlinear photonic molecular materials in structured photonic environments.