Second-order perturbational analysis of the interaction between graphite sheets

The interlayer interactions in the double- and triple-layer graphite slabs stacked in the ABAB fashion are analyzed from second-order perturbation theory. The interlayer interactions derive from van der Waals interaction that can be partitioned into attractive dispersion and repulsive forces. The attractive interaction is due to the electron density fluctuations originating from the mixtures between occupied and unoccupied orbitals that lie close in energy near the Fermi level while the repulsive interaction derives from the interlayer interactions of occupied orbitals. The interlayer interaction in the double-layer graphite slab is mainly dominated by the highest occupied crystal orbital (HOCO) with a strong antibonding nature between the sheets, which results in a large interlayer spacing in comparison with 3.35 Å in crystalline graphite [J. Am. Chem. Soc. 122 (2000) 11871]. In contrast to the double-layer graphite slab, the triple-layer slab has nonbonding orbitals, which significantly weaken the repulsive interaction caused by the HOCO that is out of phase between the sheets. The nodal properties of the nonbonding orbitals in the triple-layer slab is responsible for the attractive interaction between the sheets in the triple-layer slab. As a consequence, the triple-layer slab has a small spacing compared with that of the double-layer slab.