Ab initiostudy of the structural, electronic, and optical properties of ultrathin lead nanowires

Abstract

An ab initio study of the energetic, structural, electronic, and optical absorption properties of the 26 lead nanowires, ${\mathrm{Pb}}_{n}$ $(n=1,18)$ having different $m$-gonal $(m=1--8)$ cross sections has been made in the density functional theory in local density approximation considering also the spin-orbit coupling (SOI). There are four groups of the stable structures: planar, caged, pyramidal, and helical. The binding energy of a nanowire, in general, increases with the coordination number except in those systems where the nearest neighbors are comparatively far away. A 14-Pb hexagonal helical configuration has maximum stability followed by the heptagonal, other hexagonal, and pentagonal wires. All the nanowires are metallic. The exceptions are the 2-Pb and 3-Pb semiconducting nanowires. A large number of the conduction channels leading to high quantum ballistic conduction are seen for a number of the $m$-gonal $(m=4--8)$ configuration wires. The calculated optical absorption without and with the SOI are quite different in terms of the number of the absorption peaks which are enhanced approximately by a multiplying factor of 2 by the SOI. The $m$-gonal $(m=4--8)$ nanowires reveal multipeaked, strong, and extended optical absorption over the whole visible region. Our analysis of the experimental data for the Pb samples that have been fabricated by Romanov points towards the occurrence of the 2-Pb ladder chains.