Embedded configuration interaction description of CO on Cu(111): Resolution of the site preference conundrum

We apply an embedded configuration interaction (ECI) theory to study the adsorption of CO on Cu(111), a well-known case where standard approximations to exchange-correlation within density functional theory (DFT) fail qualitatively to predict the correct site preference and quantitatively overbind CO to both hollow and on-top sites. In ECI theory, the chemisorption region is represented by a cluster consisting of CO and a few (4-10) nearby Cu atoms, with the effect of the periodic metallic background accounted for by an effective one-electron embedding potential derived from periodic DFT. The embedded cluster is then treated using accurate ab initio multireference configuration interaction methods for electron correlation. The ECI theory yields a CO adsorption site preference and binding energy in excellent agreement with experiment, without resorting to ad hoc corrections.