Effect of layer stacking on the electronic structure of graphene nanoribbons

The evolution of electronic structure of graphene nanoribbons (GNRs) as a function of the number of layers stacked together is investigated using ab initio density functional theory (DFT), including interlayer van der Waals interactions. Multilayer armchair GNRs (AGNRs), similar to single-layer AGNRs, exhibit three classes of band gaps depending on their width. In zigzag GNRs (ZGNRs), the geometry relaxation resulting from interlayer interactions plays a crucial role in determining the magnetic polarization and the band structure. The antiferromagnetic (AF) interlayer coupling is more stable compared to the ferromagnetic (FM) interlayer coupling. ZGNRs with the AF in-layer and AF interlayer coupling have a finite band gap, while ZGNRs with the FM in-layer and AF interlayer coupling do not have a band gap. The ground state of the bilayer ZGNR is nonmagnetic with a small but finite band gap. The magnetic ordering is less stable in multilayer ZGNRs compared to that in single-layer ZGNRs. The quasiparticle GW corrections are smaller for bilayer GNRs compared to single-layer GNRs because of the reduced Coulomb effects in bilayer GNRs compared to single-layer GNRs.