Abstract
Modeling of spectral properties of extended chemical systems, such as the case of a solute in a solvent, is often performed based on so-called hybrid models in which only part of the complete system is given a quantum chemical description. The remaining part of the system is represented by an embedding potential treating the environment either by a discrete or continuum model. In order to successfully make use of minimally sized quantum chemical regions, the embedding potential should represent the environment as authentic as possible. Here, the importance of exactly such an accurate description of the embedding potential is investigated by comparing the performance of the polarizable embedding scheme against larger-sized full quantum mechanical calculations. Our main conclusion is that as long as the solute and solvent do not overlap in their absorption spectra, the polarizable embedding approach shows results consistent with full quantum chemical calculations. For partly overlapping absorption spectra, the polarizable embedding approach can furthermore successfully be expanded within a Frenkel exciton approach based on only economical monomeric quantum chemical calculations. Thus, by extending the polarizable embedding scheme to the exciton picture, it is possible to cover computations of the whole absorption spectrum and still reduce the computational cost compared to costly cluster calculations.
Highlights
In recent years, a lot of effort has been devoted to development and benchmarking of computational procedures aimed at calculating molecular response properties of chromophores in their natural environments such as in a solvent, a protein or another bio-structure
Because molecular response properties are coupled to the electronic structure of the molecule in question, such calculations require at least a partial quantum mechanical treatment, which in many cases is challenging due to the generally large size of the considered molecular systems and the associated computational cost of such calculations
It is here noted that the spectrum is shifted 0.1–0.2 eV to the right for all peaks and that using TIP3P water fails to reproduce the shoulder observed on the central peak at around 6.2 eV
Summary
A lot of effort has been devoted to development and benchmarking of computational procedures aimed at calculating molecular response properties of chromophores in their natural environments such as in a solvent, a protein or another bio-structure. The continued concerted development of novel efficient algorithms and computer architectures has made it possible to perform quantum chemistry (QC) calculations on very big systems as highlighted recently in Ref.[1] the procedure of increasing the size of the system treated with quantum mechanics (QM) still suffers from relative high computational cost especially when studying bio-molecular systems,[2] where effects of nuclear dynamics can play a crucial role. Such dynamics is handled by coupling the quantum mechanical method to e.g. molecular dynamics. Such problems usually show up in finite cluster representations of the system considered and leads, in the case of solute-solvent systems, to artificially edge effects.[4]
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