Abstract
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 quantum 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 the quantum many-body effects. To test our theory, we have computed the STM spectra of magnetic cobalt monomers and dimers adsorbed on a metallic copper surface and successfully compared our results to recent available experimental data.