We introduce a density functional theory/molecular mechanical approach for computation of linear response properties of molecules in heterogeneous environments, such as metal surfaces or nanoparticles embedded in solvents. The heterogeneous embedding environment, consisting from metallic and nonmetallic parts, is described by combined force fields, where conventional force fields are used for the nonmetallic part and capacitance-polarization-based force fields are used for the metallic part. The presented approach enables studies of properties and spectra of systems embedded in or placed at arbitrary shaped metallic surfaces, clusters, or nanoparticles. The capability and performance of the proposed approach is illustrated by sample calculations of optical absorption spectra of thymidine absorbed on gold surfaces in an aqueous environment, where we study how different organizations of the gold surface and how the combined, nonadditive effect of the two environments is reflected in the optical absorption spectrum.

We generalize a density functional theory/molecular mechanics approach for heterogeneous environments with an implementation of quadratic response theory. The updated methodology allows us to address a variety of non-linear optical, magnetic and mixed properties of molecular species in complex environments, such as combined metallic, solvent and confined organic environments. Illustrating calculations of para-nitroaniline on gold surfaces and in solution reveals a number of aspects that come into play when analyzing second harmonic generation of such systems--such as surface charge flow, coupled surface-solvent dynamics and induced geometric and electronic structure effects of the adsorbate. Some ramifications of the methodology for applied studies are discussed.

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.

A new algorithm for the evaluation of two-electron repulsion integrals optimized for high contraction degrees is derived. Both the segmented and general contraction versions of the algorithm show significant theoretical performance gains over the asymptotically fastest algorithms published in the literature so far. A preliminary implementation of the algorithm shows good agreement with the theoretical results and demonstrates substantial average speedups in the evaluation of two-electron repulsion integrals over commonly used basis sets with varying degrees of contraction with respect to a mature, highly optimized quantum chemical code.