Comparative Study of Interfacial Electron Transfer between Molecules and Metal Surfaces Using Constrained Density Functional Theory

Interfacial electron transfer between molecules and metal surfaces plays a decisive role in surface chemistry, which can be largely coupled with energy-transfer processes at molecule–metal interfaces. Here, we employ constrained density functional theory to systematically investigate interfacial charge transfer between various molecules and metal surfaces, including CO/Ag(111), N 2 /Au(111), N 2 /Pt(111), and CO 2 /Cu(111) systems, and discuss the roles of molecular vibration and orientation as well as surface electronic structure in determining the associated charge transfer states. We find that the spatial orientation of CO significantly modulates electronic coupling and charge localization, with the carbon-terminated configuration favoring the electron acceptor. Similarly, the parallel orientation of N 2 is found to be more favorable than the perpendicular orientation to accept an electron, leading to a lower energy for the negative ion. Comparative studies of N 2 on Au(111) and Pt(111) reveal that the higher density of states near the Fermi level in Pt enhances the stabilization of transient anions. In the case of CO 2 on Cu(111), electron transfer preferentially couples to the bending mode, followed by the symmetric and antisymmetric stretches. This study establishes a foundation for further exploration of electron-mediated vibrational energy transfer and reaction dynamics on metal surfaces.