  Recent experimental results have demonstrated the ability of monolayer
MoS$_2$ to efficiently generate second harmonic fields with susceptibilities
between 0.1 and 100 nm/V. However, no theoretical calculations exist with which
to interpret these findings. In particular, it is of interest to theoretically
estimate the modulus of the second harmonic response, since experimental
reports on this differ by almost three orders of magnitude. Here, we present
single-particle calculations of the second harmonic response based on a
tight-binding band structure. We compare directly with recent experimental
findings and include in the discussion also spectral features and the effects
of multiple layers.
