Various properties (geometry, band structure and the totally symmetric vibrational modes) of small diameter single-walled carbon nanotubes (SWCNTs) were investigated by first principles density ...functional theory (DFT) calculations. We studied 40 different SWCNTs, including 14 chiral ones down to diameters of 0.3 nm. The behavior of small diameter tubes is significantly different from that of the usual, larger diameter nanotubes. The diameter is larger than what is expected from simple folding. The bond lengths and bond angles are not uniform. The strong σ–π rehybridization effect modifies the band structure with respect to the tight binding approximation. The frequency of the radial breathing mode (RBM) shows a softening with decreasing diameter as compared to the usual 1/
d dependence and this softening depends strongly on chirality. RBM frequencies are further modified by the coupling with high frequency totally symmetric modes in a non-negligible way for small diameter tubes. These deviations cannot be described by a smooth monotonic function of the diameter.
Heating of organic molecules, for example, fullerenes encapsulated in single walled carbon nanotubes can result in the coalescence of the molecules forming an inner tube. The growth of tubes with ...different diameters and/or chiralities can start at different places at the same time. The formation of a junction between the two different tubes depends on many parameters. A special case is when the two tubes have the same chiralities, but opposite handedness. We have shown using topological and combinatorial arguments that at least two non‐equivalent junctions can be formed in these cases, with different arrangements of the pentagons and heptagons in the junction. We optimized the geometry using first principles method and investigated the effect of the junction on the electronic density of states of the bamboo‐type nanotube.
Lattice reconstruction in twisted transition-metal dichalcogenide (TMD) bilayers gives rise to piezo- and ferroelectric moiré potentials for electrons and holes, as well as a modulation of the ...hybridization across the bilayer. Here, we develop hybrid k ⋅ p tight-binding models to describe electrons and holes in the relevant valleys of twisted TMD homobilayers with parallel (P) and antiparallel (AP) orientations of the monolayer unit cells. We apply these models to describe moiré superlattice effects in twisted WSe2 bilayers, in conjunction with microscopic ab initio calculations, and considering the influence of encapsulation, pressure, and an electric displacement field. Our analysis takes into account mesoscale lattice relaxation, interlayer hybridization, piezopotentials, and a weak ferroelectric charge transfer between the layers, and it describes a multitude of possibilities offered by this system, depending on the choices of P or AP orientation, twist angle magnitude, and electron/hole valley.
We study the strength of the binding of 4d and 5d transition metals on a graphene sheet in the limit of low‐ and high‐coverage using first principles density functional theory. A database of the ...binding energies is presented. Our results show that Mo, Hf, Ta, and W bind strongest to the graphene sheet. We find a charge transfer of ≈0.01 electrons per carbon atom from the transition metal to the graphene sheet.
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