Ab-initio calculations of electronic circular dichroism

We review two novel developments in theoretical and computational approaches to chiroptical spectroscopy, namely the study of the rotatory strength tensor governing anisotropic circular dichroism, and the use of quantum mechanical response theory for incorporating the effect of electron correlation in ab-initio calculations of electronic circular dichroism. Large scale ab-initio calculations of the rotatory strength tensor, using the random phase approximation, are reported for the beta-gamma unsaturated ketone norbornenone and for the helically twisted hexahelicene molecule, and the predicted anisotropy of the circular dichroism is illustrated for a number of excitations in the two molecules using a graphical approach. For the hexahelicene molecule, the computed scalar rotatory strengths and rotatory strength tensors are used to generate theoretical circular dichroism spectra. The agreement between the theoretical isotropic circular dichroism spectrum and the corresponding experimental solution spectrum is quite good, and the theoretical circular dichroism spectra for light propagating along the principal axes of the molecular inertia tensor show striking variations in signs and magnitudes relative to the isotropic spectrum.