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 simu lations on the solvation of naphthalene in acetonitrile. A semiempirical tr eatment is introduced into classical molecular dynamics simulations to deal with the electronic polarizability of the solute. We study the structure o f the solvation shell, the features of the electrostatic intermolecular int eractions, the dynamics of solute and solvent molecules and the spectral sh ifts of the solute. For this particular system it is found that the influen ce of induced electrostatic interaction on the structure of the solvation s hell is negligible. On the other hand, net induced dipolar contributions ar ise in the electrostatic interactions, in spite of the fact that the electr ic field is found to be inhomogeneous at the scale of the solute molecule. These induced dipolar interactions enhance the calculated absorption and em ission 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 dyna mics are discussed in terms of dipole and quadrupole jumps. (C) 2001 Americ an Institute of Physics.