F. Shimojo

M." Tanaka

Y. "Zempo

"Zempo,  Y.

Shimojo,  F.

Tanaka,  M."

NIFS-Repository (National Institute for Fusion Science)

§ 24. Ab initio Tight-Binding MolecularDynamics Simulation of HydrogenAdsorption on Graphite SurfaceZempo, Y. (Tsukuba Research Lab. SumitomoChemical)Shimojo, F. (Kumamoto University)Tanaka, M.carbon consisted by sp2 orbitals of the graphenechange to the sp3-like orbitals, so that thehydrogen-bonded carbon atom sticks out of thegraphene sheet. The interaction has no significantbarrier except for the second hydrogen adsorption,which has a barrier of 0.67eV. As the result, a freeatom is formed.Figure 1. Decomposition of the carbon network andformation of through adsorption of hydrogenatoms on a graphene. White and black ballsdenote hydrogen and carbon atoms, respectively.is the energy difference.References1) R.O. Jones and O. Gunnarssen, Rev. Mod. Phys. 61,689(1989)2) P. Ordejon, E. Artacho and 1. M. Soler, Phys. Rev. B53,10441(1996)3) N. Troullier and 1. L. Martins, Phys. Rev. B43,1993(1991)4) D.M. Ceperly and B. 1. Alder, Phys. Rev. Lett. 45,566(1980); 1. P. Perdew and A. Zunger, Phys. Rev. B23,5048(1981)5) L. Klienman and D. M. Bylander, Phys. Rev. Lett. 48,1993(1991)To investigate the phenomena in the intermediateregion between plasma and materials, the ab initiomolecular dynamics simulation provides accurateresults. It has been applied to various fields [1] sincethe Car·Parrinello method was invented. Recently, thefully self-consistent density functional method, basedon a linear combination of atomic orbital (LCAO)basis set, has been developed. The two-center integralsare dynamically determined by the norm-conservingpseudopotentials and the pseudo-atomic wavefunctions. This technique is simple enough to describecomplicated structures of the many-body system [3].We applied this code to the adsorption process thatoccurs on a graphite surface, which is used as thematerial of the frrst wall in fusion devices [4]. It isalso interesting in the filed of epitaxial growth bymeans of the chemical vapor deposition. In both theprocesses, the atomic hydrogen interacts with thegraphite surface.Our calculation is performed using the ab initiomolecular dynamics method within the framework ofthe local density functional theory [1]. We employedthe norm-conserving pseudopotential by Troullier andMartins in the separable form [5]. The energy cut-offis 200 Ryd. In the Brillouin zone sampling, we choosea r (gamma) point to keep the degree of freedom inthe atomic structure optimization in the simulatingsystem. In the present calculation, graphite is replacedby a slab of graphite sheet (graphene) in a unit cell(7.41 X8.56X 13.86A3) for simplicity. The graphenein the unit cell contains 24 carbon atoms. All atoms inthe cell are relaxed and optimized in the coordinateand energy spaces.We have observed the methane forming process inthe graphene: Fig. 1 shows the decomposition of thegraphene sheet through interactions with hydrogenatoms. With these interactions, the bonds around the392

Ab initio Tight-Binding Molecular Dynamics Simulation of Hydrogen Adsorption on Graphite Surface

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