  Both SnS and SnSe have been experimentally and theoretically confirmed as
topological crystalline insulators in native rocksalt structure. Here, phononic
structure, thermodynamical properties and temperature dependent electron-phonon
interaction (EPI) have investigated for both the materials in rocksalt phase.
Previously performed theoretical studies have predicted the phase instability
of SnS in this crystal structure at ambient condition. But, after a detailed
study performing on the phonon calculation of SnS, we have predicted the phase
stability of SnS with considering the Sn 4$p$ orbitals as valence states in
$ab-initio$ calculation. The importance of long range Coulomb forces along with
the themodynamical properties are also described in detailed for both
materials. The preliminary evidence of topological phonon is found along X-W
direction, where the linear band touching is observed as compared to type II
Weyl phononic material ZnSe. The topological phase transition is seen for these
materials due to EPI, where non-linear temperature dependent bandgap is
estimated. The predicted value of transition temperature for SnS (SnSe) is
found to be $\sim$700 K, where after this temperature the non-trivial to
trivial topological phase is seen. The strength of EPI shows more stronger
impact on the electronic structure of SnS than SnSe material. The reason of
non-linear behaviour of bandgap with rise in temperature is discussed with the
help of temperature dependent linewidths and lineshifts of conduction band and
valence band due to EPI. The present study reveals the phase stability of SnS
along with the comparative study of thermal effect on EPI of SnS and SnSe.
Further, the possibility of temperature induced topological phase transition
provides one of important behaviour to apply these two materials for device
making application.
