The adsorption of mercury-species on relaxed and rumpled CaO (0 0 1) surfaces investigated by density functional theory

This research examines the importance of several computational choices in modeling mercury species adsorption on calcium oxide surfaces and is the second in a series of papers. The importance of surface relaxation was tested and it was found that adsorption energies changed for HgCl₂, moving adsorption from being at the borderline of physisorption and chemisorption to being strongly chemisorbed. Results for Hg and HgCl were unaffected. A second computational choice, that of the cluster or periodic model size was tested in both the plane of the model (4∈×∈4 or 5∈×∈5 model sizes) and for the depth (two or three layers). It was found that the minimum cluster size for handling mercury adsorption was 5∈×∈5 and that only two layers of depth were needed. The energetic results show that rumpled CaO surfaces will only weakly physisorb elemental mercury, but could be used to capture HgCl₂ from coal combustion flue gases, which is in agreement with limited experimental data.