  Employing density functional theory-based methods, we investigate monolayer
and bilayer structures of hexagonal SnS$_{2}$, which is recently synthesized
monolayer metal dichalcogenide. Comparison of 1H and 1T phases of monolayer
SnS$_{2}$ confirms the ground state to be the 1T phase. In its bilayer
structure we examine different stacking configurations of the two layers. It is
found that the interlayer coupling in bilayer SnS$_{2}$ is weaker than that of
typical transition-metal dichalcogenides (TMDs) so that alternative stacking
orders have similar structural parameters and they are separated with low
energy barriers. Possible signature of the stacking order in SnS$_{2}$ bilayer
has been sought in the calculated absorbance and reflectivity spectra. We also
study the effects of the external electric field, charging, and loading
pressure on the characteristic properties of bilayer SnS$_{2}$. It is found
that (i) the electric field increases the coupling between the layers at its
prefered stacking order, so the barrier height increases, (ii) the bang gap
value can be tuned by the external E-field and under sufficient E-field, the
bilayer SnS$_{2}$ can become semi-metal, (iii) the most favorable stacking
order can be switched by charging and (iv) a loading pressure exceeding 3 GPa
changes the stacking order. E-field tunable bandgap and easy-tunable stacking
sequence of SnS$_{2}$ layers make this 2D crystal structure a good candidate
for field effect transistor and nanoscale lubricant applications.
