First-principles thermodynamic description of hydrogen electroadsorption on the Pt(111) surface

The issue of hydrogen (H) electroadsorption on Pt(111) is revisited to settle its theoretical description within the conventional ultrahigh vacuum (UHV) surface modeling and the semilocal Kohn-Sham level of the density functional theory (DFT). By performing a converged DFT calculation, we have confirmed nearly degenerated nature of H on the fcc hollow site (Hfcc) and H on the top site (Htop) when the nuclei are treated classically, while Hfcc is significantly more stable when the zero-point energy correction is applied. Relative abundance of the Hfcc over Htop was investigated by performing a Monte Carlo simulation using a lattice gas model parameterized by the DFT calculation. By comparing the calculated results with recent cyclic voltammetry data, we found good agreement between theory and experiment but minor discrepancy exists in that the H-H interaction is underestimated by ~ 10%. Possible origin of the discrepancy is the hydration effect neglected in our model although we cannot exclude the possibility that error of the semilocal approximation within DFT will also play a role.