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Abstract. The existence of second-order structural phase transition in the SnS at a pressure of 16 GPa has been proved theoretically. The calculation is performed using the plane-wave pseudopotential approach to density-functional theory within the local-density approximation (LDA) with the help of the ABINIT software package. The abrupt change in volume compression with unit cell volume continuous change of the crystal is the clear evidence of the second-order phase transition. It is shown that the phase transition is caused by the softening of the low-frequency fully symmetric interlayer mode with increasing pressure. As a result, displacement type phase transition (PT) take place with the change of translational symmetry of the crystal from the simple orthorhombic to the base-centered orthorhombic (P cmn (

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Half-metallic properties of TlCrS 2 , TlCrSe 2 and hypothetical TlCrSSe have been investigated by first-principles all-electron full-potential linearized augmented plane wave plus local orbital (FP-LAPW+lo) method based on density functional theory (DFT). The results of calculations show that TlCrS 2 and TlCrSSe are half-metals with energy gap (E g ) ~0.12 ev for spin-down channel. Strong hybridization of p-state of chalchogen and d-state of Cr leads to bonding and antibonding states and subsequently to the appearance of a gap in spin-down channel of TlCrS 2 and TlCrSSe. In the case of TlCrSe 2 , there is a partial hybridization and p-state is partially present in the DOS at Fermi level making this compound nearly half-metallic. The present calculations revealed that total magnetic moment keeps its integer value on a relatively wide range of changes in volume (-10%  10%) for TlCrS 2 and TlCrSSe, while total magnetic moment of TlCrSe 2 decreases with increasing volume approaching to integer value 3μB.