On the Nature of Inter layer Interactions in a System of Two Graphene Fragments

With the help of the quantum chemistry methods, we have investigated the nature of interlayer interactions between graphene fragments in different stacking arrangements (AA and AB). We found that the AB stacking pattern, as the ground state of the system, is characterized by the effective interband orbital interactions which are barely present in the AA. Their vanishing induces electronic decoupling between the graphene layers, so that the bonding interaction Delta E-oi between the flakes is drastically reduced from -0.482 to -0.087 eV as the stacking pattern is changed from AB to AA. The effective way to improve the bonding interaction between layers preserving the same AA lattice order is to induce rotation of the layer. As the flake is rotated, the bonding interactions are improved mostly due to suppresion of the Pauli repulsion which in turn increases the interlayer orbital interactions, while the interband part of those remain negligible on the whole range of the rotation angle. The Pauli repulsion is also found to be the main force that moves the two fragments apart as the stacking pattern is changed from AA to AB. This enhances the equilibrium interlayer distance, which for the AA staking is larger than the established value for the AB stacking (3.4 angstrom).