A multiconfiguration self-consistent field/molecular dynamics study of the (n→π)1 transition of carbonyl compounds in liquid water

A model is presented for the electrostatic component of solvatochromic shifts in vertical electronic excitation energies. The model, which makes use of the mean-field approximation, combines quantum mechanics (QM) in the description of the solute molecule and molecular mechanics (MM) in the description of the solvent. The method is implemented at the multiconfigurational self-consistent field level. We present illustrative applications to the (n→π*)1 transitions of formaldehyde, acetaldehyde, and acetone in liquid water. The solvent shifts obtained compare well with other ab initio QM/MM calculations and when the electron correlation components are included with the experimental solvent shift, but differ from the results obtained with semiempirical QM/MM and continuum models.