One of the main features of topological trystalline insulators (TCI) is the existence of zero-gap Dirac-like states on certain high-symmetry crystal facets. The factor which is responsible for the existence of nontrivial topological phase is mirror symmetry with respect to {110} crystallographic planes. Recently, in number of experiments for (Pb,Sn)Se it was discovered that apart of zero-gap surface states there are also surface states with nonzero energy gap. Scanning Tunneling Microscopy measurements revealed relative displacement of cation and anion sublattices in the first monolayer of the crystal. In this way the crystal has the mirror symmetry with respect to (110) plane but loses the symmetry with respect to perpendicular (-110) plane. This explains simultaneous presence of zero and nonzero energy gaps in four valleys hosting TCI states. The reason of the existence of such displacements is not clear and that is why in the first part of our work we performed many ab initio simulations of the layers for some of the IV-VI semiconductors. We did not find any displacement in the plane parallel to the surface. Instead we found displacements in the direction perpendicular to the surface which are in agreement with the theoretical and experimental literature data. In the second part of the work we studied electron dispersion relations for different contents of tin in thick layers of (Pb,Sn)Se. From our earlier works we know that increasing the tin content, the transition from normal to TCI state does not appear for well defined tin concentration but these two phases are separated by Weyl semimetal phase. What is interesting this Weyl region is also characterized by surface electron dispersion relation of quite a different character than in normal and TCI states.