Electronic structure of the Cu3Au(1 1 1) surface

Using the NRL-tight binding method, we investigate the electronic structure of the unrelaxed Cu3Au(1 1 1) surface. The tight binding parameters were determined by fitting to LDA calculations and found to reproduce the surface energy, bulk elastic constants and bulk phonon modes. The surface electronic band structure shows electronic states at the center of the Brillouin zone, within −0.1 Ry of the Fermi level, in agreement with available photoemission data. For these states, we give an interpretation and characterization of the contributions of the s, p and d electrons of the Cu and Au atoms. Charge calculations on each atom indicate that upon formation of Cu3Au there is charge transfer from the Au atoms to the Cu atoms in agreement with previous X-ray experiments. The Cu3Au(1 1 1) surface atoms are found to gain charge compared to the bulk system, and the Au atoms regain some of the charge that they lost upon formation of bulk Cu3Au. Despite the fact that this tight binding Hamiltonian was fitted to bulk properties of the Cu3Au system, it is able to accurately describe the main features of the Cu3Au(1 1 1) surface, suggesting that this method is reliable for studying binary intermetallic alloy surfaces.