Table of contentsSummaryIntroductionThe calculation methodConclusionSummaryThe existence of a second-order structural phase transition in SnSe at a pressure of 10 GPa has been proven theoretically. The calculation is carried out using the plane wave pseudopotential approach to density functional theory within the framework of local density approximation (LDA) using the ABINIT software package. The abrupt change in the bulk modulus together with the continuous change in the unit volume of the crystal cell is clear evidence of the second-order phase transition. It is shown that the phase transition is caused by the softening of the fully symmetric low-frequency interlayer shear mode with increasing pressure. As a result, a displacement-like phase transition (PT) takes place with the change in 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 Should Not Be Banned”? Get the 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 results in compression or tension in thin films. Due to the difference in the thermal expansion coefficients of the film and the substrate, biaxial deformations also take place. The lattice structural parameters and electronic properties of crystals change significantly under applied pressure, and this must be taken into account when developing various devices. Thus, the study of the effect of pressure on the structural, elastic and electronic parameters of compounds is of great interest. In recent years, great efforts have been made to create photovoltaic devices from non-toxic materials with simple and inexpensive 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 short-circuit current density, suggesting that this material found in abundance in the earth could be a valuable component in future photovoltaic devices. As we know, two experimental studies on the effect of hydrostatic pressure on SnSe structural parameters have been published in recent years. Mossbauer measurements were performed on SnSe under hydrostatic pressure between 0.001 and 55 kbar and temperature and pressure induced phase transition in compounds IV-VI. No phase transition was detected in this work. In this paper, we theoretically study the possibility of a phase transition at pressure in the SnSe crystal. 2. The SnSe crystal structure belongs to the group of A4B6 type layered semiconductor compounds. The crystal structure consists of four atomic planes in sequence Sn-Se-Se-Sn. The unit cell of the crystal contains two layers linked by the operation of inversion symmetry. The intralayer bonds are predominantly covalent in character, while the bond between layers is weak and is likely of the van derWaals type. The two types of atoms occupy the positions (4c): ±(x; y, 1/4) and ±(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 carried out using the software package.