  We show that a simple first-principles correction based on the difference
between the singlet-triplet CO excitation energy values obtained by 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 2$\pi$* orbital found recently {[Kresse {\em et
al.}, Physical Review B {\bf 68}, 073401 (2003)]}. Converged DFT calculations
underestimate the CO singlet-triplet excitation energy $\Delta E_{\rm S-T}$,
whereas coupled-cluster and CI calculations reproduce the experimental $\Delta
E_{\rm S-T}$. The dependence of $E_{\rm chem}$ on $\Delta E_{\rm S-T}$ is used
to extrapolate $E_{\rm chem}$ 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 $\Delta E_{\rm S-T}$ value. The correction
reproduces experimental adsorption site preference for all cases and obtains
$E_{\rm chem}$ in excellent agreement with experimental results.
