Electronic and optical properties of high pressure stable phases of ZnS: Comparison of FPLAPW and PW-PP results S.K. Gupta a , S. Kumar a, ⁎, S. Auluck b a Applied Physics Department, Institute of Engineering and Technology, M. J. P. Rohilkhand University, Bareilly-243 006, India b Department of Physics, Indian Institute of Technology, Kanpur-208 016, India abstract article info Article history: Received 10 December 2009 Received in revised form 12 August 2010 Accepted 23 August 2010 Keywords: FPLAPW PW-PP GGA Electronic structure Optical properties A theoretical study of the structural phase transformation of ZnS under high pressure has been performed using first principle plane wave pseudopotential (PW-PP) and full potential linear augmented plane wave method (FPLAPW) calculation in which Zn-3d states are treated as valence states. In both methods, we have used a generalized gradiant approximation for the study of phase transformation and structural parameters. The calculated difference in lattice constants (Δα 0 ) by PW-PP and FPLAPW methods for zinc-blende, cinnabar and rocksalt structures is equal to 0.003, 0.01 and 0.001 Å respectively. There is a very good agreement between the results of PW-PP and FPLAPW calculations that shows soundness of our choice of pseudopotential. The calculated transition pressure for zinc-blende →rocksalt is in agreement with available measured data. We present calculations of the optical properties for three phases of ZnS. The band gap of different phases of ZnS decreases in order of zinc-blende →cinnabar →rocksalt mainly due to red shift of Zn-s states in the lowest conduction band. Besides, the optical band gap decreases from 2.84 eV (direct) to 0.188 eV (indirect). The shift of calculated complex dielectric function ε 2 (ω) for zinc-blende →cinnabar →rocksalt is also discussed in details of optical transition that occurred in different phases. © 2010 Elsevier B.V. All rights reserved. 1. Introduction ZnS, an important member of the II–VI group, has attracted much attention due to the polymorphic structural transformation and optoelectronic applications in blue-light regime which make it more useful than the other members of this group. Although several research groups [1–11] have investigated the structural phase transition using different methods, there is still a scope of discussion about the existence of phases and their transition pressures. It is believed that ZnS in the zinc-blende (ZB) or wurtzite (WZ) phase transforms to rocksalt (RS) structure and then to β-Sn structure. However, Desgreniers et al. [1] have reported that the WZ phase transforms to the ZB structure prior to a transition at higher pressure to the RS phase. Pan et al. [2] have measured the transition pressure of 11.5 GPa for the WZ →ZB and 16 GPa for the ZB →RS transitions by using the energy dispersive X-ray diffraction technique. On the other hand, several research groups have calculated the phase transitions theoretically using different methods. Miao et al. [3] have calculated the ZB →RS structural phase transition equal to 14.5 GPa using a pseudopotential technique. Gangadharan et al. [7] showed that the phase transition ZB →RS occurs at 15.5 GPa using the tight binding linear muffin tin orbital (TB-LMTO) method. Qteish and Parrinello [10] using the pseudopotential method, obtain that phase transition ZB →RS occurs at 15 GPa. Jaffe et al. [6] showed that the ZB →RS phase transition occurs at 16.1 GPa using the linear combina- tion of atomic orbitals (LCAO) method. Amjad et al. [9] used the pseudopotential approach to confirm the stability of cinnabar (Cin) structure between ZB and RS structures in ZnS. Qteish et al. [11] used full potential linear muffin tin orbital method to confirm that there is no stable intermediate Cin phase of ZnS under high pressure. The previous calculation of Chen et al. [8] had used non local ultrasoft pseudopotential [12] along with Perdew–Wang exchange correlation to find the transition pressures for the different phases of ZnS and the obtained phase transition pressure ZB →RS using two methods namely the common tangent of energy volume curves and the condition of equal enthalpies gave different values of the transition pressure equal to 17.5 GPa and 15.4 GPa respectively. We were motivated to perform calculations to clarify the following: in this paper, we have shown through two ab-initio methods PP-PW and FPLAPW that the transition pressure is the same either using the common tangent of energy volume curve or the condition of equal enthalpies thus removing the discrepancy noted in Ref. [8]. There are limited full potential first principle calculations for the high pressure ZnS phases. In this paper we fill this gap. We also present a comparison of the transition pressures using the PW-PP and FPLAPW methods. As there is a dearth of calculations of the optical properties of ZnS in the high pressure phases, we report calculations of the optical properties using the FPLAPW method. Pressure is an important parameter which allows an increasing material density by reducing the volume. Optics Communications 284 (2011) 20–26 ⁎ Corresponding author. Tel./fax: +91 581 2524232. E-mail address: drsudhirkumar.in@gmail.com (S. Kumar). 0030-4018/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2010.08.046 Contents lists available at ScienceDirect Optics Communications journal homepage: www.elsevier.com/locate/optcom