Correlating Optical and Structural Properties of CO on Transition Metal Surfaces

We present an optical study based on the quasiparticle self-consistent GW (QSGW) approximation combining structural information taken from density functional theory (DFT) to elucidate spectral features of CO adsorbed on Pt(111) and Cu(111). Optical information and structural arrangement of the adsorbed CO are correlated by varying both site positions and CO coverage as compared to experimental studies (..theta.. = 1/4 to ..theta.. = 1/2). This enables us to resolve key spectral features of both occupied and unoccupied molecular states at various adsorbate coverages, comparing theory to experiment. Using experimental data as benchmarks, we show the theory compares well with available data. Its predictive power provides a new path to infer information about the structure of CO from optical information and can help to predict the presence of other little understood adsorbates such as an OCCO dimer that may be relevant to mechanistic pathways for reduction of CO2 to high value C2+ products. This new approach complements total energy calculations and also fills a void in DFT-based theory that is known to be an unreliable predictor of the energetics of CO on transition metal surfaces.