Structural Stabilities of Ordered Nb₄ Clusters on the Cu(111) and Cu(100) Surfaces

Based on first-principles calculations, we show that very high-density periodic arrays of Nb₄ clusters with both the tetrahedron and quadrangle configurations can be stably absorbed on the Cu(111) and Cu(100) surfaces, with the quadrangle configurations more stable than the tetrahedron ones. The strong covalent bonding between atoms within the Nb₄ clusters contributes to the stability of Nb₄ adsorptions on the Cu surfaces. The energy barriers for the tetrahedron to the quadrangle-Nb₄ on Cu(111) and (100) are around 1.21eV and 0.94eV/cluster, respectively. The stable adsorption of high-density Nb₄ on these surfaces should have important applications.