  Recently, the quantum spin Hall effect has been predicted in (111)-oriented
thin films of SnSe and SnTe topological crystalline insulators. It was shown
that in these films the energy gaps in the two-dimensional band spectrum depend
in an oscillatory fashion on the layer thickness -- the calculated topological
invariant indexes and edge state spin polarizations show that for films 20-40
monolayers thick a two-dimensional topological insulator phase appears. Edge
states with Dirac cones with opposite spin polarization in their two branches
are obtained for both materials. However, for all but the (111)-oriented SnTe
films with an even number of monolayers an overlapping of bands in
$\overline{\Gamma}$ and $\overline{\mathrm{M}}$ diminishes the final band gap
and the edge states appear either against the background of the bands or within
a very small energy gap. Here we show that this problem in SnSe films can be
removed by applying an appropriate strain. This should enable observation of
the Quantum Spin Hall effect also in SnSe layers.
