First-principles extrapolation method for accurate CO adsorption energies on metal surfaces

We show that a simple first-principles correction based on the difference between the singlet-triplet CO excitation energy values obtained by density-functional theory (DFT) and high-level quantum chemistry methods yields accurate CO adsorption properties on a variety of metal surfaces. We demonstrate a linear relationship between the CO adsorption energy and the CO singlet-triplet splitting, similar to the linear dependence of CO adsorption energy on the energy of the CO 2pi* orbital found recently [Kresse , Phys. Rev. B 68, 073401 (2003)]. Converged DFT calculations underestimate the CO singlet-triplet excitation energy DeltaE(S-T), whereas coupled-cluster and configuration-interaction (CI) calculations reproduce the experimental DeltaE(S-T). The dependence of E-chem on DeltaE(S-T) is used to extrapolate E-chem for the top, bridge, and hollow sites for the (100) and (111) surfaces of Pt, Rh, Pd, and Cu to the values that correspond to the coupled cluster and CI DeltaE(S-T) value. The correction reproduces experimental adsorption site preference for all cases and obtains E-chem in excellent agreement with experimental results.