  Despite the experimental successes of Scanning Tunneling Microscopy (STM) and
the interest in more complex magnetic nanostructures, our present understanding
and theoretical description of STM spectra of magnetic adatoms is mainly
phenomenological and most often ignores many-body effects. Here, we propose a
theory which includes a microscopic description of the wave functions of the
substrate and magnetic adatoms together with quantum many-body effects. To test
our theory, we have computed the STM spectra of magnetic Cobalt monomers and
dimers adsorbed on metallic Copper surfaces and succesfully compared our
results to recent available experimental data.
