Stability and Electronic\nStructure of Double-Walled\nTransition Metal Dichalcogenide Nanotubes

The stability and electronic properties of double-walled\nMX<sub>2</sub> nanotubes (M = Mo, W; X = S, Se, or Te) are investigated\nusing density functional theory. It is shown that each of these double-walled\ntransition metal dichalcogenide nanotubes exhibits metastable structures\nwhen the intertube distance is sufficiently small, relative to the\ncorresponding 2D TMD monolayer. As the intertube interactions are\ndominated by van der Waals interactions, the extent of this metastability\nis primarily determined by the polarizability of the chalcogen. The\nband structure and band gaps of these structures show that the band\ngap of the material predominantly arises from inner-tube →\ninner-tube excitations between Mo/W states. Most interestingly, the\nband gap of the inner-tube was found to change significantly, by up\nto ∼0.3 eV, depending on the distance between the tubes, due\nto the radial compression caused by the outer-tube.