A QM/MM Approach Using the AMOEBA Polarizable Embedding: From Ground State Energies to Electronic Excitations

A fully polarizable
implementation of the hybrid quantum mechanics/molecular
mechanics approach is presented, where the classical environment is
described through the AMOEBA polarizable force field. A variational
formalism, offering a self-consistent relaxation of both the MM induced
dipoles and the QM electronic density, is used for ground state energies
and extended to electronic excitations in the framework of time-dependent
density functional theory combined with a state specific response
of the classical part. An application to the calculation of the solvatochromism
of the pyridinium N-phenolate betaine dye used to
define the solvent ET(30) scale is presented. The results
show that the QM/AMOEBA model not only properly describes specific
and bulk effects in the ground state but it also correctly responds
to the large change in the solute electronic charge distribution upon
excitation.