Theoretical investigations of bond properties in graphite and graphitic silicon

Within the local-density approximation, the interlayer binding and the electronic properties of graphite and “graphitic” Si have been determined. For graphite, the optimized equilibrium lattice constant agrees well with the experimental value. The role of ${2p}_z$ orbitals $(\pi$ states) turned out to be 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 binding 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 applied to fit an additional Lennard-Jones-type empirical potential to be included in classical molecular-dynamics simulations. In contrast to that, the calculated energy pathways for “graphitic” Si show an extended region of minima within the range of $a=3.84\mathrm{}\AA$ and for c varying from 5.50 to $6.68\AA$ having two lower levels, which indicates chemisorption and physical absorption. The obtained electronic density distribution demonstrates that the atoms in “graphitic” Si tend to form a structure with metal-like electron distributions. Nevertheless, a Lennard-Jones potential with restricted validity may be fitted to describe the weak long-range behavior, too.