IndexAbstractIntroductionThe calculation methodConclusionAbstractThe existence of a second-order structural phase transition in SnSe at a pressure of 10GPa has been demonstrated 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 sudden change in the bulk modulus together with the continuous change in the unit cell volume of the crystal is the clear evidence of the second-order phase transition. The phase transition was shown to be caused by the softening of the low-frequency fully symmetric interlayer shear mode with increasing pressure. Consequently, the shift-type phase transition (PT) occurs with the change of the translational symmetry of the crystal from simple orthorhombic to base-centered orthorhombic. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay Introduction Modern microelectronics based on the use of thin films grown on various substrates. A mismatch in the lattice parameters of the film and substrate causes compressive stress in thin films. Due to the difference in thermal expansion coefficients of the film and the substrate, biaxial deformations also occur. The structural parameters of the lattice and the electronic properties of the crystals change substantially under applied pressure and this should be taken into account in the development of various devices. Therefore, studying the effect of pressure on the structural, elastic and electronic parameters of compounds is of great interest. In recent years, great efforts have been aimed at creating photovoltaic devices with non-toxic materials and simple, low-cost production technology. In this regard, semiconductor compounds of the A4B6 group were very promising. Preliminary solar cell devices incorporating SnSe nanocrystals in a poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] matrix demonstrate significant improvement in quantum efficiency and density of short-circuit current, suggesting that this earth-abundant material could be a valuable component in future photovoltaic devices. As we know, in recent years two experimental studies have been published on the effect of hydrostatic pressure on SnSe structural parameters. Mossbauer measurements were performed on SnSe under hydrostatic pressure in the range of 0.001 to 55 kbar and temperature- and pressure-induced phase transition in compounds IV–VI. In these works no phase transition was detected. In this article, we theoretically investigate the possibility of phase transition at one pressure in SnSe crystal. 2. The SnSe crystal structure belongs to the group of layered semiconductor compounds of the A4B6 type. The crystalline structure consists of four atomic planes in the sequence Sn-Se-Se-Sn. The unit cell of the crystal contains two layers linked by the symmetry reversal operation. The intralayer bonds are predominantly covalent in nature, while the bond between the layers is weak and presumably of the van derWaals type. Both types of atoms occupy positions (4c): ±(x; y, 1/4) is ±(1/2 − x, 1/2 + y, 1/4), (see Fig. 1). The lattice parameters are: a = 4. 445Å, b = 11. 501Å, c = 4. 153Å, xSn = 0. 1035, ySn = 0. 1185, xSe = 0. 4819, ySe = 0. 8548. The method calculationAll calculations are performed using the ABINIT software package. The equilibrium parameters at zero temperature were obtained by minimizing.