Paper SS1-TuM11
CO Chemisorption on Cu(111) via Embedded Configuration Interaction Theory

Tuesday, October 16, 2007, 11:20 am, Room 608

Although density functional theory (DFT) is often considered the electronic structure method of choice to study surfaces, situations exist where DFT fails, e.g. strongly correlated electrons and descriptions of unoccupied states. As an example, CO adsorption on Cu(111) is poorly described within DFT because the CO bond to Cu(111) involves Cu back-donation to the empty CO 2pi* orbitals, which are at too low an energy in DFT, leading to an overestimation of pi back-bonding. Measurements at low coverage are consistent with on-top site CO adsorption on Cu(111), whereas pseudopotential-based DFT methods predict hollow site adsorption, due to the overestimation of the importance of pi-back-bonding. In this work, we study CO/Cu(111) with a density-based embedding strategy, where a local region of interest, described by accurate ab initio quantum chemistry calculations, is embedded into a background described by DFT. The region of interest is represented by a cluster of atoms that includes CO and nearby metal atoms. A self-consistent, DFT-based embedding potential accounts for the effect of the background on this cluster. Since ab initio quantum chemistry methods, e.g. configuration interaction (CI), give a better description of the CO LUMO, we expect an improvement on the description of CO chemisorption. We will present site preferences and adsorption energies from embedded CI, as well as comparing to periodic DFT and finite cluster calculations.