Computational Insights into Reorientation-Mediated Water Diffusion on Pt(111): Comparison to H₂O/Pd(111)

Understanding water diffusion on metal surfaces is essential for catalysis, corrosion, and scientifically significant electrochemical processes. Using density functional theory (DFT) calculations, we found that water reorientation on metal surfaces plays a critical role in modulating orbital competition modes, coherent HOMO couplings, electron transfer, and vibronic couplings. However, Pd(111) and Pt(111) show significantly different abilities to modulate the reorientational water diffusion. Water diffusion on Pt(111) obviously breaks the orientation-dependent orbital competition discovered on Pd(111) and shows unbalanced orbital competition controlling both H-down and H-up water diffusion except for HVP, where balanced orbital competition takes place. Furthermore, the electronic rule of orientation-dependent coherent HOMO coupling modes identified on Pd(111) shows a breakdown for the Pt(111)-supported HDW mechanism, which, on the contrary, exhibits reduced amplitudes of coherent HOMO couplings. Likewise, the orientational dependence of net electron transfer obtained on Pd(111) also shows a breakdown for the Pt(111)-supported HUF mechanism, which instead shows increased oscillation amplitudes of the net electron transfer pattern. Moreover, the coupled vibronic couplings between the water bending mode and HOMO couplings observed in the H₂O/Pd(111) system are unexpectedly absent in H₂O/Pt(111), where only the decoupled vibronic couplings between symmetric HOH stretching (phonons) and coherent HOMO couplings are observed in its HVP mechanism. Our investigations have revealed the bonding nature of water-metal interactions during transient surface diffusion, which can be valuable for understanding electronic catalytic mechanisms involving water on metal surfaces.