  We investigate the coupling of different quantum-embedding approaches with a
third molecular-mechanics layer, which can be either polarizable or
non-polarizable. In particular, such a coupling is discussed for the multilevel
families of methods, in which the system is divided into an active and an
inactive orbital spaces. The computational cost of the resulting three layers
approaches is reduced by treating the long-range interactions at the classical
level.The methods developed are tested against the calculation of the
excitation energies of molecular systems in aqueous solution, for which an
atomistic description of the environment is crucial to correctly reproduce the
specific solute-solvent interactions, such as hydrogen bonding. In particular,
we present the results obtained for three different moieties, acrolein,
pyridine and para-nitroaniline, showing that an almost perfect agreement with
experimental data can be achieved when the relevant physico-chemical
interactions are included in the modeling of the condensed phase.
