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A combination of Monte Carlo simulation and quantum mechanics calculation is used to study properties, structure and spectroscopy of molecules in solution. All properties are obtained as statistical averages using uncorrelated structures generated by the Monte Carlo simulation. The auto-correlation function of the energy is calculated and used in the correlation analysis. Examples include the solvatochromic shift of the n–π ∗ transition of formaldehyde and pyridine in water. A detailed and systematic analysis is made starting from the hydrogen bond shell and extending up to the bulk limit. Long range effects are found to be of importance for the total solvatochromic shift. Short range, hydrogen bond, effects are seen to alter the dipole moment of the chromophore both in direction and module, having an effect on the outer solvation shells. A careful analysis is made of the possible structural changes induced by a solvent in merocyanine dyes. The hyperpolarizability of phenol blue is shown to vary with the resonance between the two, neutral and charge-separated, forms, having a pronounced maximum as obtained experimentally. This indicates that phenol blue undergoes structural changes in polar solvents.

Dipole moment, static dipole polarizability and hyperpolarizability are calculated for MgH with high-order many-body perturbation theory and coupled-cluster methods using large basis sets. At the highest levels, CCSD(T), the calculated values are 0.533 a.u. (dipole moment), 65.3 a.u. (average polarizability), −10.3 a.u. (polarizability anisotropy) and 580.7 a.u. (first hyperpolarizability). The derivatives of the dipole moment and dipole polarizability with respect to the internuclear separation are also calculated. These gradients are used to predict the infrared absorption intensity. Raman scattering activity and Rayleigh and Raman depolarizations of light scattering by diatomic MgH. The cross section for Raman scattering is predicted. The degree of depolarization of the Raman scattered light is found to be very large for natural, planar and circular polarizations.