CO bonded to platinum: effects of semi-core polarization

The CO–platinum bond is systematically investigated with respect to metal semi-core polarization for platinum carbonyls and CO bonded to Pt(1 1 1). This is an issue of renewed interest owing to the recent observation [J. Phys. Chem. B 105 (2001) 4018] that several implementations of the density functional theory predict a three-fold hollow site to be the preferred adsorption site of CO on Pt(1 1 1), whereas experimental low coverage data show that atop is the stable adsorption site. The present calculations reveal clear effects of semi-core polarization in structural, energetic and vibrational properties. In general, the effects are more pronounced in atop compared with bridge and hollow configurations. For the carbonyls, fair agreement with experimental gas phase data is obtained if semi-core polarization effects are taken into account. Allowing for 5s5p relaxation, reduces the atop site preference from ∼0.2 to ∼0.1 eV for CO/Pt(1 1 1).