11 An Evaluation of Density Functional Theory for CO Adsorption on Pt(111)
201
Fig. 11.2 The projected
d-band center energies for
(a) Pt 7–3 and (b) Pt 9–9–9
clusters as respect to the ratio
of HF exchange energy
ratio of HF exchange energy. When increasing the ratio of HF exchange energy, the
projected DBC energies are decreased. Our results also show that the top-DBC energies are ca. 0.9 and 0.4 eV smaller than the fcc-DBC energies except for the case
of M06HF in Pt 9–9–9 . For M06HF, the top-DBC energy is almost the same with the
fcc-DBC energy. As a reasonable expectation, the top-DBC energy should be the
same with the fcc-DBC energy in real extended Pt surface, and thus the M06HF can
give the better description among the 21 functionals used in this study. Comparing
the σ -top-DBC and π -top-DBC energies, it can be found that the σ -top-DBC energy is higher than the π -top-DBC energy in most cases. However, the differences
between σ -top-DBC and π -top-DBC energies are reduced as increasing Pt cluster
size and adding more ratio of HF exchange energy. For the case of M06HF in Pt 7–3
and M06HF, BMK, wB97 and wB97X in Pt 9–9–9 , the π -top-DBC energies become
higher than the σ -top-DBC energies.