| Abstract
| - In this study, we present calculations of the circular dichroism (CD) spectra of complexes between achiraland chiral molecules. Nonzero rotational strengths for transitions of the nonchiral molecule are induced byinteractions between the two molecules, which cause electronic and/or structural perturbations of the achiralmolecule. We investigate if the chiral molecule (environment) can be represented only in terms of its frozenelectron density, which is used to generate an effective embedding potential. The accuracy of these calculationsis assessed in comparison to full supermolecular calculations. We can show that electronic effects arisingfrom specific interactions between the two subsystems can reliably be modeled by the frozen-densityrepresentation of the chiral molecule. This is demonstrated for complexes of 2-benzoylbenzoic acid with(−)-(R)-amphetamine and for a nonchiral, artificial amino acid receptor system consisting of ferrocenecarboxylicacid bound to a crown ether, for which a complex with l-leucine is studied. Especially in the latter case,where multiple binding sites and interactions between receptor and target molecule exist, the frozen-densityresults compare very well with the full supermolecular calculation. We also study systems in which acyclodextrin cavity serves as a chiral host system for a small, achiral molecule. Problems arise in that casebecause of the importance of excitonic couplings with excitations in the host system. The frozen-densityembedding cannot describe such couplings but can only capture the direct effect of the host electron densityon the electronic structure of the guest. If couplings play a role, frozen-density embedding can at best onlypartially describe the induced circular dichroism. To illustrate this problem, we finally construct a case inwhich excitonic coupling effects are much stronger than direct interactions of the subsystem densities. Thefrozen density embedding is then completely unsuitable.
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