Properties of Adsorbed Oxygen Forms on a Defective Ag(111) Surface. DFT Analysis

Abstract

A cluster model of an Ag12–3O (AS_V) adsorption center using layered silver oxide as a prototype is proposed. The model includes a cation vacancy V on the Ag(111) surface and oxide type subsurface oxygen atoms O_ox. Density functional theory (DFT) (B3LYP/LANL1MB approximation) is used to analyze the electronic structure of AS_V and oxygen adsorption on this center, AS_V+O → AS–O. As shown by the calculations, the adsorbed oxygen is associated with the subsurface oxygen atoms O_ss to form structures similar to metal ozonides — Ag–O_ss–O_ep–O_ss–Ag–O_ox–Ag, containing electrophilic oxygen O_ep along with the oxide oxygen O_ox. The optical spectra of the AS_V and AS–O centers were calculated by the configuration interaction method with single excitations (CIS). For AS_V, the most intense absorption bands were obtained in the region 500-700 nm. Oxygen association is accompanied by a sharp decrease in spectrum intensity in the range 600-700 nm and an increase in the intensity of the peak at 500 nm. Vibration frequencies and (IR) intensities were determined for the AS_V and AS–O centers. The AS_V center exhibits a characteristic spectrum in the region 350-500 cm^–1, which corresponds to the frequency spectrum of the surface oxide Ag₂O. For associated oxygen forms (AS–O center), the calculations predict additional peaks around 980, 640 and 230 cm^–1. These peaks are due to the vibrations of the O_ss–O_ep–O_ss structural unit, stabilized at the cation vacancy.