TDDFT calculations of NEXAFS spectra of model systems for SO2 adsorbed on the MgO(100) surface

The time-dependent density functional theory approach has been employed to simulate the core excitation spectra of model systems for the adsorption of SO2 on the MgO (100) regular surface. All of the edges, sulfur K and L edges and oxygen K edge, have been considered in the calculations. Cluster models are adopted to describe the different interaction modes of SO2 With the acidic and basic sites of the surface. The main aspects of the MgO surface modeling have been considered, and their influence on the calculated spectra of the adsorbed molecule has been analyzed. The results show that the method provides a viable tool for obtaining excitation energies and oscillator strengths in this big system and allows for the investigation of the origin of the spectral features. The comparison between the spectra calculated for the adsorbate models and the spectrum of the free SO, allows for the discussion of the nature of the adsorbate-substrate interaction (physi- or chemisorption) in terms of the differences in their core excitation spectra.