First-principles study of the electronic properties of transition metal nitride surfaces

Transition metal nitride (TMN) surfaces are investigated by using the first-principles molecular dynamics method. Electronic and structural properties of five systems (TiN, ZrN, NbN, HfN and TaN(0 0 1)-1×1) are calculated. The optimized surface structures and electronic properties (charge densities, electronic band structures, work function, etc.) are obtained. All calculated electronic states of surfaces are metallic. By the full structural optimization of the surface, the nitrogen and transition metal atoms on the top layer move outward and inward, respectively. This trend of atomic displacements on the outermost layer is similar to our previous results of transition metal carbide (TMC) surfaces. In most surfaces, the values of the work function for the TMN surfaces are lower than those for the TMC surfaces. The values of the work function for relaxed ZrN, NbN, HfN and TaN surfaces are lower than those for unrelaxed (ideal) surfaces. This lowering of the work function is different from our previous results of TMC surfaces.