Solvent Effects on Rotatory Strength Tensors. 1. Theory and Application of the Combined Coupled Cluster/Dielectric Continuum Model

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In this article we present the first theoretical study of solvent effects on the rotatory strength tensor. The system chosen is solvated formaldehyde for which only one tensor element is nonvanishing, and the solvent is modeled as a linear, homogeneous, and isotropic dielectric continuum. We present results using both an equilibrium and a nonequilibrium description of the solvent. Four illustrative solvents (ethyl ether, acetone, methanol, and water) are considered together with the corresponding results for formaldehyde in vacuum. We utilize the following ab initio methods: the coupled cluster model including singles and doubles (CCSD) and the coupled cluster second-order approximate singles and doubles (CC2). Furthermore, we compare the coupled cluster results with the corresponding uncorrelated self-consistent-field (SCF) results. In addition to the rotatory strength tensor we also present solvent effects on the low-lying electronic excitation energies and corresponding ordinary intensities using both the length and velocity gauges. We find that both correlation and solvent effects have a significant influence on the transition properties. The introduction of the solvent is, in some cases, found to result in a sign change of the rotatory strength tensor elements which clearly demonstrates the importance of a proper description of the solvent influence on this property.