Hybrid Complex Polarization Propagator/Molecular Mechanics Method for Heterogeneous Environments

We introduce a hybrid complex polarization propagator/molecular mechanics method for the calculation of near-resonant and resonant response properties of molecules in heterogeneous environments, which consist of a metallic surface, or nanoparticle, and a solvent. The applicability and performance of the method is demonstrated by computations of linear absorption spectra of p-nitroaniline physisorbed at a gold/dimethyl sulfoxide interface in the UV/vis and near-carbon-K-edge regions of the spectrum. It is shown that the shift of absorption cross-section induced by the heterogeneous environment varies significantly depending on the nature of the excited states encountered in the targeted frequency region as well as on the actual size of the resonant frequencies, and that the solvent component of the heterogeneous environment is responsible for the major part of the environmental shift, especially in the higher frequency range of the carbon K-edge region.