OPTOELECTRONICS AND ADVANCED MATERIALS – RAPID COMMUNICATIONS Vol. 8, No. 7-8, July – August 2014, p. 724 - 726 First principles study of band structure and density of states of rare earth oxytellurides R 2 O 2 Te (R=La, Ce, Pr and Nd) ASIF MAHMOOD a , SHAHID M. RAMAY a , Y. SAEED b,* Department of Chemical Engineering, College of Engineering, King Saud University, P.O. Box 800, Riyadh 11421, Saudi Arabia a Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 800, Riyadh 11421, Saudi Arabia b Department of Physics, G. C. University Faisalabad, Allama Iqbal Road, Faisalabad, Punjab 38000, Pakistan The electronic structure calculations of the rare earth oxytellurides of formula Ln2O2Te have been investigated by using full potential linearized augmented plane method within Coulomb corrected local spin-density approximation LSDA+U. The LSDA+U calculations yield first time the indirect-gap semiconductors nature (Eg1.82 eV) for all Ln2O2Te, while no experimental data available. The substantial covalent bonds between Ln and O and less covalent bond between Ln and Te coexist in the materials. These materials have potential application in magneto-optoelectronic industry. (Received February 25, 2014; accepted July 10, 2014) Keywords: Density Functional Theory, LDA+U, Ferromagnetic, Band structure, Rare earth 1. Introduction In the past years lanthanides-containing material received much attention because of their diverse electrical, optical and chemical properties. They can be successfully used in lasers, wide gap electro-luminescent devices, light emitting diodes, scintillator detectors, and as efficient host for the design of phosphorescent materials [1-5]. The rare earth oxytellurides belong to this interesting series of materials. The rare earth oxytellurides have interesting physical properties and are very promising in practical regards [6, 7]. Least studied among these compounds are the REM oxytellurides due to technical difficulties in their preparation [8]. From the pioneering work published by Domange et. al. [7] and more recent investigations by Llanos et. al. [9], it has been established that the rare earth oxytellurides Ln 2 O 2 Te (Ln = La, Ce, Pr, and Nd) crystallize in the tetragonal phase with space group I4/mmm. The crystal structure can be described as an anti- ThCr 2 Si 2 -type structure, where the Ln +3 cations are surrounded by eight anions (4O 2- and 4Te 2- ) arranged as a distorted square anti prism. The polyhedral are connected in a way that maintains the three dimensional coherence of the crystal structure and the charge balance [8]. Recently Llanos et. al. [9] reported the synthesis, the optical and magnetic properties and the electronic structure of the rare earths oxytellurides. They have performed the electronic structure calculations within Generalized Gradient approximation (GGA) only for La 2 O 2 Te by using the SIESTA code and suggest an indirect band gap. In contrast to the large number of study devoted to the study of rare earth oxysulphide and oxyselenide, oxytellurides are less explored. In addition, there is no theoretical information about the electronic structure particularly the band structure of the oxytellurides, for example we do not know whether the system has a direct band gap or an indirect one. Furthermore, we do not know any theoretical evidence that could explain the anisotropic refractive indices, though we can expect the property from the anisotropic crystal structure. Knowledge of electronic structure of the rare earth oxytellurides is crucial in order to understand optoelectronic process in the materials. This is why here we carry out the full potential calculations of these materials. 2. Computational details The calculations reported here were perform using the WIEN2k [10] implementation of the full-potential linear augmented plane wave (FLAPW) method in the scalar- relativistic regime. We have found in other theoretical results that LSDA+U approximation is appropriate for calculating the electronic properties of rare earth compounds [11, 12]. To describe the exchange correlation functional we have used rotationally invariant LSDA+U approximation and double counting scheme of Anisimov [13] and collaborators. The standard parameterization of the on-site Coulomb interaction involves two parameters U and J. The role of J reduces to merely re-normalizing the U value. Therefore we can set J=0 and quote just the U value. We have used the U values for La 2 O 2 Te, Ce 2 O 2 Te,