First-principles calculations of the structural, electronic and elastic properties of ZnWO 4 and CdWO 4 single crystals at the ambient and elevated pressure M.G. Brik * , V. Nagirnyi, M. Kirm Institute of Physics, University of Tartu, Riia 142, Tartu 51014, Estonia highlights graphical abstract < Structural, electronic, elastic prop- erties of CdWO 4 , ZnWO 4 were calculated. < Pressure effects on the electronic and structural properties were modeled. < Complete sets of elastic constants for CdWO 4 , ZnWO 4 are reported. 0 5 10 15 20 4.35 4.40 4.45 4.50 4.55 4.60 4.65 CdWO 4 , GGA CdWO 4 , LDA ZnWO 4 , GGA ZnWO 4 , LDA Band gap E g , eV Pressure, GPa article info Article history: Received 1 July 2012 Received in revised form 14 October 2012 Accepted 1 November 2012 Keywords: Electronic materials Ab initio calculations Crystal structure Elastic properties abstract Two technologically important tungstate crystals e CdWO 4 and ZnWO 4 e are studied theoretically using the plane wave based first-principles calculations. The optimized crystal structures were used to calculate the structural, electronic and elastic properties of both materials under varying hydrostatic pressure. It was shown that the band gaps, which are direct at ambient pressure, turn into indirect ones in both compounds in the pressure range from 5 to 10 GPa, whereas the values of the band gaps themselves depend only slightly on the applied pressure. Differences in compressibility along the crystallographic axes and the WeO, CdeO, ZneO chemical bonds were revealed and quantified by calculating the pressure coefficients for all these characteristic distances. The first estimations of the complete elastic tensor constants for both materials are reported. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction The application of hydrostatic pressure is a powerful tool for studying the crystal and electronic structure of a material. The scope of application of the results comprises a wide variety of areas starting from the geology-related studies (see, e.g., Ref. [1] and references therein) to the physics of impurity centres [2] and excitons [3,4] in solids. In particular, hydrostatic pressure influ- ences the radiative decay of free and self-trapped excitations as well as energy transfer processes [4]. The amount of literature devoted to the experimental and theoretical study of the influence of pressure on the lattice parameters, electronic and optical prop- erties of crystals is remarkable. In the last decades, the first-prin- ciples calculations within the frames of the density functional theory (DFT) using the generalized gradient approximation (GGA) and the local density approximation (LDA) became available [5,6]. Starting from the basic knowledge on material structure these methods allow predicting a number of its characteristics concern- ing the elastic properties of the lattice and behaviour under the uniaxial and hydrostatic pressure. This type of calculations is still rare and such a large class of practically important solids as complicated oxides like, e.g., tungstates and molybdates of alkali- * Corresponding author. Tel.: þ372 7374751; fax: þ372 738 3033. E-mail address: brik@fi.tartu.ee (M.G. Brik). Contents lists available at SciVerse ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys 0254-0584/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matchemphys.2012.11.011 Materials Chemistry and Physics 137 (2013) 977e983