Adsorption behaviors of Cs and I atoms on the graphite surface by the first-principles

The adsorption behaviors of radioactive Cesium and Iodine nuclides on the graphitic surface in the high temperature gas-cooled reactor have been studied by the first-principles and statistic physics. It turns out that Cs atom prefers to be absorbed at the hollow of carbon hexagonal cell by 1.44 eV while I atom likes to site on the vertex of the hexagonal cell, right above carbon atoms with the adsorption energy of 0.54 eV. Electronic structure analysis reveals that Cs donates 0.81e of its 6s and 5p states to graphite substrate while the 5p state of I accepts 0.5e from carbon atoms. The variation of adsorption rate of Cs and I atoms with temperature and pressure is presented using a model of grand canonical ensemble.