Size-Dependent Stability of Nonhelical and Helical Copper Nanowires Using Density Functional Theory and Density-Functional-Based Tight-Binding Methods

The structural stability and electronic transport properties of Cu nanowires (Cu NWs) with diameter of 0.2–3.0 nm are reported for the future application in flexible displays and flexible solar cell. The density functional theory (DFT) and density-functional-based tight-binding (DFTB) approaches have been combined to systematically discover the ballistic transport and diffusive transport of ultrathin Cu NWs in the nanoscale. Because the electrical conductance is originally from both quantum and diffusive mechanisms, our DFT calculations firstly show that with the increasing of diameters, the quantum conduction (G) of both nonhelical and helical nanowires are increased. Secondly, our DFTB calculations reveal that as the diameter of nanowires increases above 2.1 nm, stability and diffusive transport properties of nonhelical are better than that of helical. It is further proved by comprehensively considering the results of the energy, density of states (DOS), transmission and electron potential properties.