Bulk and Surface Electronic Structure of the Layered Sub-Nitrides Ca₂N and Sr₂N

The binary sub-nitrides M2N (M = Ca and Sr) have the anti-CdCl2 layered structure. First-principles calculations show that these sub-nitrides are best described as ionic compounds with one electron in the “van der Waals gap” between the calcium (strontium) layers. The nitrogen 2p states show rather localized character with a bandwidth of about 2 eV. The compounds have a quasi-two-dimensional electronic structure with a cylindrical Fermi surface perpendicular to the layer direction. Calculations also show that the surface M2N slab has density of N 2s, 2p states shifted toward to a lower energy (about 1 eV) with respect to the bulk. These layered compounds may have an application as cathode material for polymer LED devices.