Theoretical investigations of bond properties in graphite and graphitic silicon

Abstract

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 $(\ensuremath{\pi}$ 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 $a=3.84\AA{}$ 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.