Hydrogen Adsorption in Potassium-Intercalated Graphite of Second Stage: An ab Initio Molecular Dynamics Study

We present an ab initio molecular dynamics study on hydrogen adsorption in potassium-intercalated graphite of second stage. The simulation utilizes the ultrasoft pseudopotenals plane wave method under local density functional approximation. The optimized lattice structures and the calculated H2 adsorption energy are in excellent agreement with experiments. The simulation also well reproduces the previously observed lattice expansion due to H2 uptake. The dynamics investigations reveal that not only the adsorbed hydrogen molecules but also the intercalated potassium atoms are highly mobile and assume a variety of two-dimensional configurations. The hydrogen dynamics is essentially chaotic within a layer of about 1.4 Å thickness centered between the graphite sheets, with a closest C−H distance of about 2.2 Å.