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 2π* orbital found recently [Kresse et al., Phys. Rev. B 68, 073401 (2003)]. Converged DFT calculations underestimate the CO singlet-triplet excitation energy ΔE_S-T, whereas coupled-cluster and configuration-interaction (CI) calculations reproduce the experimental ΔE_S-T, The dependence of E_chem on ΔE_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 ΔE _S-T value. The correction reproduces experimental adsorption site preference for ali cases and obtains E_chem in excellent agreement with experimental results.