Combined multireference configuration interaction/molecular dynamics approach for calculating solvatochromic shifts:: Application to the nO→π* electronic transition of formaldehyde

A combined quantum mechanics/molecular mechanics method is described here for considering the solvatochromic shift of excited states in solution. The quantum mechanical solute is described using high level multireference configuration interaction methods (MRCI), while molecular dynamics is used for obtaining the structure of the solvent around the solute. The electrostatic effect of the solvent is included in the quantum description of the solute in an averaged way. This method is used to study solvent effects on the n(O) -> pi* electronic transition of formaldehyde in aqueous solution. The effects of solute polarization, basis sets, and dynamical correlation on the solvatochromic shift, and on dipole moments, have been investigated.