We report the production of covalently bonded selenium double-helices within the narrow cavity inside double-wall carbon nanotubes. The double-helix structure, characterized by high-resolution transmission electron microscopy and X-ray diffraction, is completely different from the bulk atomic arrangement and may be considered a new structural phase of Se. Supporting ab initio calculations indicate that the observed encapsulated Se double-helices are radially compressed and have formed from free Se atoms or short chains contained inside carbon nanotubes. The calculated electronic structure of Se double-helices is very different from the bulk system, indicating the possibility to develop a new branch of Se chemistry.

Gueorguiev, Van der Waals stacks of few-layer h-AlN with graphene: an ab initio study of structural, interaction and electronic properties, 2016, Nanotechnology, (27) Here, by employing vdW-corrected density functional theory calculations, we investigate structure, interaction energy, and electronic properties of van der Waals stacking sequences of few-layer h-AlN with graphene. We find that the presence of a substrate such as graphene induces enough interlayer charge separation in h-AlN, favoring a graphite-like stacking formation. We also find that the interface dipole, calculated per unit cell of the stacks, tends to increase with the number of stacked layers of h-AlN and graphene.

Carbon nanowires made of long linear atomic chains have attracted considerable interest due to their potential applications in nanoelectronics. We report a theoretical characterization of assemblies with good prospects for chemical synthesis made of two coronene molecules (graphene-like pieces) bridged by carbon linear chains with distinct sizes and parities. Our calculations are performed within all-electron density functional theory. We examine the effects of two conformations (syn and anti) of the terminal anchor pieces, representing energy minima for these systems, on the properties of the carbon chains. The calculated electronic states reveal that simplified chemical models such as those based on cumulenes or polyynes are not appropriate to describe the linear chains with sp2 terminations. For these types of atomic chains, we find that the electronic ground state of the odd-numbered chains is spin polarized. Vibrational properties of all these chains are studied by calculating Raman scattering and infrared spectra. We show that syn and anti conformations of the graphene-like terminations lead to important effects in the vibrational features of the chains, detectable by the Raman light-scattering depolarization.