Iodated activated carbons were found to be effective for the mercury uptake from coal combustion flue gas. However, the detailed mechanism of mercury binding remains unclear. The adsorption mechanisms of mercury iodine on carbonaceous surface were studied by density functional calculations. A cluster model of five benzene rings was used to represent the active sites. The Mulliken bond population and total atomic charges analysis were performed to better understand the interaction of mercury-iodine species with surface. The results show that the binding of mercury-iodide species on surface include several adsorbing and desorbing processes. HgI is strongly adsorbed on the surface and the preferred adsorption mode is Hg-down mode. HgI is very stable existing on surface because the evolution of HgI is highly endothermic process. HgI2 adsorption is not stable, and some of the geometrical configurations of the intermediates show the dissociation of HgI2. The dominant interaction pathway is the dissociation of HgI2 with the binding of HgI and I on carbon surface. (C) 2016 Elsevier B.V. All rights reserved.