  We derive, from an empirical interaction potential, an analytic formula for
the elastic bending modulus of single-layer MoS2 (SLMoS2). By using this
approach, we do not need to define or estimate a thickness value for SLMoS2,
which is important due to the substantial controversy in defining this value
for two-dimensional or ultrathin nanostructures such as graphene and nanotubes.
The obtained elastic bending modulus of 9.61 eV in SLMoS2 is significantly
higher than the bending modulus of 1.4 eV in graphene, and is found to be
within the range of values that are obtained using thin shell theory with
experimentally obtained values for the elastic constants of SLMoS2. This
increase in bending modulus as compared to monolayer graphene is attributed,
through our analytic expression, to the finite thickness of SLMoS2.
Specifically, while each monolayer of S atoms contributes 1.75 eV to the
bending modulus, which is similar to the 1.4 eV bending modulus of monolayer
graphene, the additional pairwise and angular interactions between out of plane
Mo and S atoms contribute 5.84 eV to the bending modulus of SLMoS2.
