Registry-dependent interlayer potential for graphitic systems

Standard applications of density functional theory (the local density approximation (LDA) and the generalized gradient approximation (GGA)) without nonlocal corrections do not adequately describe the exfoliation energy of graphite. The GGA, in particular, does not show any binding at physically meaningful interlayer distances. However, the {\it variation} in the energy under interlayer shifts, defined predominantly by the overlap of $\pi$ orbitals, is nearly identical in the two approximations and appears to be much more sound than previously suspected. We combine these results with experimental information on the exfoliation energy to create an improved registry-dependent classical potential for the interlayer interaction in graphitic structures.