Coupled molecular dynamics/semiempirical simulation of organic solutes in polar liquids. I. Naphthalene in acetonitrile

In this paper we present coupled quantum mechanical/molecular dynamics simulations on the solvation of naphthalene in acetonitrile. A semiempirical treatment is introduced into classical molecular dynamics simulations to deal with the electronic polarizability of the solute. We study the structure of the solvation shell, the features of the electrostatic intermolecular interactions, the dynamics of solute and solvent molecules and the spectral shifts of the solute. For this particular system it is found that the influence of induced electrostatic interaction on the structure of the solvation shell is negligible. On the other hand, net induced dipolar contributions arise in the electrostatic interactions, in spite of the fact that the electric field is found to be inhomogeneous at the scale of the solute molecule. These induced dipolar interactions enhance the calculated absorption and emission shifts and contribute up to 40% to the electrostatic spectral shifts. They also modify or even dominate the fluctuations of the solute-solvent interaction and thus the solvation response. Both shifts and solvation dynamics are discussed in terms of dipole and quadrupole jumps. (C) 2001 American Institute of Physics.