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 HgCl(2), 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 HgCl(2) from coal combustion flue gases, which is in agreement with limited experimental data.