Structural Stability and Electronic and Optical Properties of Coinage-Metal (4, 2) Alloy Nanotubes: A First-Principles Study

Using first-principles calculations, we have systematically investigated the structural stability and the electronic and optical properties of bimetallic Ag−Au, Cu−Au, and Cu−Ag (4, 2) alloy nanotubes (NTs). We found that the tip-suspended Ag−Au and Cu−Au alloy NTs were stable structures due to the existence of local minima in both the binding energies and the string tensions variation with their unit-cell lengths and that the stability was enhanced when the content of Au was increased. However, a tip-suspended Cu−Ag alloy NT would be difficult to form in future experiments. We also found that both the relativistic effect of elemental gold and the string tension applied by the tip contacts play important roles in suppressing effectively the self-purification effect, leading to the formation of these coinage alloy NTs. The quantum conductance of the stable alloy NTs is increased by 1G₀ as compared with that of the corresponding pure coinage-metal NTs.