Sonia Coriani

Analytic ab initio calculations of coherent anti-Stokes Raman scattering (CARS)

We present a theory for the analytic calculation of frequency-dependent polarizability gradients, and apply the methodology to the calculation of coherent anti-Stokes Raman scattering (CARS). The formalism used is based on an open-ended theory for the calculation of frequency-dependent molecular response properties of arbitrary order, also including contributions from perturbation-dependent basis sets. An important feature of our approach is the close connection between the formalism--which is fully matrix-based in an atomic orbital basis--and the implementation, allowing for the rapid implementation of higher-order molecular properties. Care is taken to allow the formalism to be utilized with linearly-scaling Hartree-Fock and density-functional theory codes. By avoiding the evaluation of responses due to geometry distortions, only 9 response equations need to be solved for the calculation of the CARS intensities, independent of the size of the molecular system. The theory is illustrated by calculations on a set of polyaromatic hydrocarbons using a DFT/B3LYP force field and Hartree-Fock polarizability gradients. Good agreement with the experimental CARS spectra of these compounds is obtained.

Ab initio calculation of magnetic circular dichroism

We discuss the ab initio calculation of all terms contributing to a magnetic circular dichroism (MCD) spectrum—i.e., A, B, and C terms—and give an overview of the most recent methods that have been introduced for calculating these different contributions. Among them, we highlight the use of the complex polarization propagator approach because it may give direct access to the A and B terms of MCD. We also briefly discuss how ab initio calculations for analyzing experimental MCD spectra can be used to gain insight into the electronic excited states of molecules.

The Cotton-Mouton effect of gaseous CO2, N2O, OCS and CS2. A cubic response multiconfigurational self-consistent field study

An extended ab initio study of the Cotton-Mouton effect of CO2, N2O, OCS, and CS2, employing correlated wave functions expanded in correlation consistent basis sets as large as t-aug-cc-pVTZ and an ...

Ab Initio Study of the Magneto‐Optical Rotation of Diastereoisomers

Experimental studies on the natural optical activity and Faraday rotation of the three different stereoisomers of tartaric acid were reported recently by Ruchon et al. [Chem. Phys. Lett. 2005, 412, 411]. The authors noted that the Faraday rotation of the meso (R,S) system differed from those of the (S,S) and (R,R) enantiomers, and derived a simple dipole-dipole interaction model to describe what they claim to be a new property. We present the results of both density functional theory (DFT) and coupled cluster calculations for a structurally elementary model system composed of two chiral carbon atoms presenting three diastereoisomers (C(2)H(2)Cl(2)F(2)), as well as a detailed DFT study of the natural and magnetic-field-induced optical rotation of tartaric acid. The effects of electron correlation, basis set, and conformational flexibility are analyzed. It is found that the specific Faraday rotations of the chiral (R,R) and meso forms of tartaric acid (for lambda=632.8 nm) differ by about 3 %, a value which is quite close in magnitude-but of opposite sign-to that obtained with the simplified model proposed by Ruchon and co-workers.