International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 03 Issue: 04 | Apr-2016 www.irjet.net p-ISSN: 2395-0072 © 2016, IRJET | Impact Factor value: 4.45 | ISO 9001:2008 Certified Journal | Page 1408 INVESTIGATION OF A7 TO SIMPLE CUBIC PHASE TRANSITION OF ARSENIC BY FIRST PRINCIPLE STUDIES S.C.R.Roshan 1 , Lavanya Kunduru 2 1 Asst. Professor, Department of Physics, RGUKT, Basar, Telangana, India 2 Asst. Professor, Department of Physics, RGUKT, Basar, Telangana, India ---------------------------------------------------------------------***--------------------------------------------------------------------- Abstract - In the present work, we report investigation of the crystal structure of arsenic under compression, focusing mainly on the pressure-induced A7 → simple cubic ȋscȌ phase transition. The two-atom rhombohedral unit cell is subjected to pressures ranging from 0 GPa to 50 GPa; for each given pressure, the cell lengths , angles and the atomic positions are allowed to vary until the relaxed structure is obtained. The nearest and next-nearest neighbor distances give indication of the structural phase transition. Calculations are performed using the local density approximation (LDA) and the PBE and PW91 generalized gradient approximations for the exchange-correlation functional using QUANTUM ESPRESSO The A7 → sc transition is found to occur at 30GPa-40GPa, no volume discontinuity is observed across the transition in any of the three cases. k-point grids as dense as 8×8×8 enable us to present reliably converged results for the A7 → sc transition of arsenic. Key Words: Structure Transition, Quantum Espresso, Pressure Studies, First Principle Calculations 1.INTRODUCTION The computational study of high-pressure behavior of materials provides the ability to properly examine the phase transitions from one structure to another of the material. The paper is organized as follows. Section I contains the background material that pertains to our study, description of the A7 phase, a quick review of the structural transformation that yields the sc phase when a sufficiently high external pressure is applied, In Section II, we mention about the methods that we have followed, In Section III, we present and discuss our results, and also comparing them with the literature. At ambient pressures, arsenic is a covalently bonded compound existing in the rhombohedral (A7) phase. The rhombohedral primitive cell of arsenic contains two atoms and is described by the length of primitive lattice vectors, a, and the angle, α, between each set of primitive lattice vectors, and by the atomic positional parameter, x , which determines the positions of the two atoms along the cell’s body diagonal. The sc lattice can be viewed as composed of two face centered cubic (fcc) lattices. Under high pressures, arsenic undergoes a transition from half metallic A7 to metallic sc.. The pressure induced A7 to simple cubic (SC) transformation in As has been proved DFT. The A7 structure is among several structures favored by the group-V elements, which are variations of the SC structure.