Theoretical investigations of bond properties in graphite and graphitic silicon

Within the local-density approximation, the interlayer binding and the elec tronic properties of graphite and ''graphitic'' Si have been determined. Fo r graphite, the optimized equilibrium lattice constant agrees well with the experimental value. The role of 2p(z) orbitals (pi states) turned out to b e twofold: contributing a major part to the binding of C atoms within basal planes, and giving a minor contribution in the form of the overlay of 2p(z ) orbitals, which leads to weaker interlayer binding. The interlayer bindin g attributed to the interaction of C-C atoms in different layers yields the calculated binding energy as a function of the lattice constants and is ap plied to fit an additional Lennard-Jones-type empirical potential to be inc luded in classical molecular-dynamics simulations. In contrast to that, the calculated energy pathways for "graphitic" Si show an extended region of m inima within the range of a = 3.84 Angstrom and for c varying from 5.50 to 6.68 Angstrom having two lower levels, which indicates chemisorption and ph ysical absorption. The obtained electronic density distribution demonstrate s that the atoms in "graphitic" Si tend to form a structure with metal-like electron distributions. Nevertheless, a Lennard-Jones potential with restr icted validity may be fitted to describe the weak long-range behavior, too.