  We study the effect of torsional deformations on the electronic properties of
single-walled transition metal dichalcogenide (TMD) nanotubes. In particular,
considering forty-five select armchair and zigzag TMD nanotubes, we perform
symmetry-adapted Kohn-Sham density functional theory calculations to determine
the variation in bandgap and effective mass of charge carriers with twist. We
find that metallic nanotubes remain so even after deformation, whereas
semiconducting nanotubes experience a decrease in bandgap with twist --
originally direct bandgaps become indirect -- resulting in semiconductor to
metal transitions. In addition, the effective mass of holes and electrons
continuously decrease and increase with twist, respectively, resulting in
n-type to p-type semiconductor transitions. We find that this behavior is
likely due to rehybridization of orbitals in the metal and chalcogen atoms,
rather than charge transfer between them. Overall, torsional deformations
represent a powerful avenue to engineer the electronic properties of
semiconducting TMD nanotubes, with applications to devices like sensors and
semiconductor switches.
