Modeling of Magnetic Circular Dichroism and UV/vis absorption spectra using Fluctuating Charges or Polarizable Embedding within a resonant-convergent response theory formalism.

In recent years computational methods based on embedding have become of increasing popularity when the aim is to introduce environmental effects into quantum chemistry calculations of molecular properties. This is due in particular to the efficiency of such methods while still retaining a high degree of accuracy compared to full quantum chemistry treatments. In the present paper we compare two popular embedding methods fluctuating charges (FQ) and polarizable embedding (PE) highlighting their similar mathematical structure. Furthermore, based on a unified formulation of the two embedding methods, we present theory and implementation of these embedding methods within resonant-convergent response theory up to the level of quadratic response. A numerical comparison between FQ and PE is presented for a set of solute solvent systems based on calculations of UV/vis and magnetic circular dichroism spectra. Overall, we find in the cases considered the FQ and PE models to perform rather similarly, especially upon introducing effects of explicit conformational sampling into the theoretical predictions.