  We consider the interaction of electromagnetic radiation of arbitrary
polarization with multi-level atoms in a self-consistent manner, taking into
account both spatial and temporal dependencies of local fields. This is done by
numerically solving the corresponding system of coupled Maxwell-Liouville
equations for various geometries. In particular, we scrutinize linear optical
properties of nanoscale atomic clusters, demonstrating the significant role
played by collective effects and dephasing. It is shown that subwavelength
atomic clusters exhibit two resonant modes, one of which is localized slightly
below the atomic transition frequency of an individual atom, while the other is
positioned considerably above it. As an initial exploration of future
applications of this approach, the optical response of core-shell
nanostructures, with a core consisting of silver and shell composed of resonant
atoms, is examined.
