  We calculate the torsional moduli of single-walled transition metal
dichalcogenide (TMD) nanotubes using ab initio density functional theory (DFT).
Specifically, considering forty-five select TMD nanotubes, we perform
symmetry-adapted DFT calculations to calculate the torsional moduli for the
armchair and zigzag variants of these materials in the low-twist regime and at
practically relevant diameters. We find that the torsional moduli follow the
trend: MS$_2$ $>$ MSe$_2$ $>$ MTe$_2$. In addition, the moduli display a power
law dependence on diameter, with the scaling generally close to cubic, as
predicted by the isotropic elastic continuum model. In particular, the shear
moduli so computed are in good agreement with those predicted by the isotropic
relation in terms of the Young's modulus and Poisson's ratio, both of which are
also calculated using symmetry-adapted DFT. Finally, we develop a linear
regression model for the torsional moduli of TMD nanotubes based on the
nature/characteristics of the metal-chalcogen bond, and show that it is capable
of making reasonably accurate predictions.
