CO/Pt(111): GGA density functional study of site preference for adsorption

Based on density functional formalism, we investigate the site preference for the adsorption of CO on Cu, Rh, Ag, Pt, and Au(111) surfaces. The exchange-correlation term was approximated by BLYP, a functional within the generalized gradient approximation (GGA) family that combines Becke's exchange functional with the Lee-Yang-Parr correlation functional. Our study shows that BLYP, although not a hybrid functional, can correctly predict the adsorption site for CO. This invalidate the general belief that only hybrid functionals are able to predict the correct site preference. We analyze our results by repeating all calculations using another well-known GGA functional, Perdew-Burke-Ernzerhof, which could trace back the origin of the success of BLYP to the different behavior of the two GGA functionals at large values of the reduced density gradients, s proportional to parallel to del n parallel to/n(3/4). This is a region where different functionals in the GGA family may legitimately behave very differently as it is poorly constrained on physical ground. Our present observation points to the possibility of further improving the accuracy of exchange-correlation functionals in the GGA family by properly constraining the remaining flexibility in the exchange-correlation kernel in this underdetermined region so as to reproduce known results in simple but critically important systems like the one studied here.