AB-INITIO STUDIES OF H CHEMISORPTION ON C(100) SURFACE

Ab initio CI theory is used to study the chemisorption of hydrogen on the C(100) surface. A three-layer cluster which consists of 19 carbon atoms and 30 hydrogen saturators is used to simulate the major features of surface reconstruction. The chemisorption of H atoms changes the surface reconstruction, shifting the dimer length from 1.51 angstrom in an H-free surface to 1.68 and 1.70 angstrom for a dimer bonded with one and two H atoms, respectively. The C-H bond energy is calculated to be 3.87 eV for the chemisorption of the first H atom and 4.14 eV for the chemisorption of the second H atom, including the corrections of zero-point vibrational energies. The C-C dimer bond energy in the monohydride phase is computed to be 1.21 eV. In forming the dihydride phase, the chemisorption of additional H atoms destroys surface dimers and changes the reconstructed 2 x 1 surface to a structure for which the interactions between surface CH2 groups are repulsive.