The stability of small helical gold nanorods: a relativistic density functional study

Multistrand 7-1 helical Au(24), Au(32), and Au(40) structures with three, four, and five gold atoms in the central strand and 21, 28, and 35 gold atoms in the coaxial tube are investigated using relativistic density functional theory. We demonstrate that these helical gold nanorods are stable structures with a rather large HOMO-LUMO gap, a large binding energy per atom, a very large vertical dissociation energy, and an extremely large electron affinity. On the basis of the atomic charges and the nature of the frontier orbitals, they are also expected to have strong selective reactivity toward electrophiles and nucleophiles. Furthermore, we show that these helical Au(n) structures and, in particular, the helical Au(40) structure are competitive energetically and chemically with respect to alternate cage and compact Au(n) structures. We consider two fragmentations of the helical Au(40) structure and perform a density of states analysis to examine both charge transfer and electronic polarization.