Prediction of electronic excited states of adsorbates on metal surfaces from first principles.

We present the first ab initio prediction of localized electronic excited states in a periodically infinite condensed phase, a heretofore intractable goal. In particular, we examined local excitations within a CO molecule adsorbed on Pd(111). The calculation allows a configuration interaction treatment of a local region, while its interaction with the extended condensed phase is described via an embedding potential obtained from periodic density functional theory. Our work lays the foundation of a microscopic understanding of photochemistry and spectroscopy on metal surfaces.