Research Article Adv. Mater. Lett. 2016, 7(5), 344-348 Advanced Materials Letters Adv. Mater. Lett. 2016, 7(5), 344-348 Copyright © 2016 VBRI Press www.vbripress.com/aml, DOI: 10.5185/amlett.2016.6105 Published online by the VBRI Press in 2016 A first-principle study of the optical properties of pure and doped LaNiO 3 Tarun Kumar Kundu*, Debolina Misra Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, India * Corresponding author. Tel: (+91) 3222-2832-96; Fax: (+91) 3222-2822-80; E-mail: tkkundu@metal.iitkgp.ernet.in Received: 21 August 2015, Revised: 06 December 2015 and Accepted: 24 March 2016 ABSTRACT Density Functional Theory (DFT) is employed to study the various optical properties of pseudo-cubic LaNiO3. As LaNiO3 is a strongly correlated material, conventional DFT like LDA or GGA and even GW approximation fail to describe, we have examined the optical spectra of this compound using GGA(PBE)+U approach. The advantage of incorporating Hubbard U in this approach is to take the strong electronic correlation in the system into account. The optical spectra of this compound are found to be consisted of the Drude peak and some high energy peaks. While the Drude peak reflects the dominant free carrier contributions at the low energy region, the high energy peaks originate from the inter-band transitions within the system. We have also studied the remarkable changes in the optical properties in Fe doped LaNiO3 (LaNi1-xFexO3), in order to probe related properties, corresponding to their applications in solid-oxide fuel cells. Our calculations have revealed that even 25% of Fe doping is adequate to trigger a first order metal to insulator transition in LaNiO3. The optical spectra of LaNi1-xFexO3 compounds are calculated using the hybrid functional HSE and the doping-induced metal to insulator transition in LaNiO3 is attributed to the altered crystal environment and electronic configuration of the compound. Copyright © 2016 VBRI Press. Keywords: DFT; optical conductivity; doping; density of states; metal insulator transition. Introduction Materials exhibiting metal-insulator transitions (MIT) are of immense importance in the field of condensed matter physics due to their applications in Mottronics and non- volatile memory devices [1-6]. Change in electrical properties in some systems is often accompanied by a transition in the magnetic state also. MIT is generally seen in transition metal oxides and doped semiconductors [7-10]. The area of Mottronics which is considered to be one of the toughest challenges in the twenty first century relies on such systems which are prone to this kind of first order transitions. It has been observed that generally correlated materials have the tendency to undergo such MIT. In these materials the complex correlation between the structure and the electronic interactions trigger huge change in their physical properties when subjected to strain, pressure, doping, electric field, variation in temperature etc. which can change the carrier concentration within the compounds [1, 7]. Depending on the difference in resistivity in the two different phases (metallic and insulating), these materials are also used in switching devices and selectors in the array-type memory devices. Rare-earth nickelates (RNiO3) is such a series of compounds where correlation plays a major role [11, 12]. The first member of this series namely LaNiO3 has recently become very popular due to its metallic nature, while rests of the members of the series are insulators [12]. The importance of LaNiO3 lies in its potential use in all the above mentioned fields, including its application as electrodes because of its metal-like behavior at room temperature [13]. Being the only conducting material in the series, although it never undergoes any MIT when subjected to temperature variation, a first order transition from metallic to an insulating state can still be obtained in this system by varying other parameters like strain, doping, oxygen-vacancy etc. [13-19]. The detailed understanding of this kind of transitions is necessary for its use in Mottronics, switching devices and for other suitable applications. Here we report the systematic theoretical investigation of the correlated metal LaNiO3 we carried out using the density functional theory, and investigate how MIT can occur in the system as a function of appropriate substitution of Ni atom by Fe atoms. The changes in the optical spectra of LaNiO3 due to the change in Ni content is analyzed and the various applications of Fe doped LaNiO3 are discussed thereof. Theory and computational details LaNiO3 is known to have a pseudo-cubic crystal structure with a small rhombohedral distortion [12]. In the cubic unit cell, the Ni atom occupies the body center position whereas the La and O atoms are at the corner and the face-center positions respectively. The structure optimization of cubic LaNiO3 is carried out using the conjugant gradient algorithm, with force convergence of 0.01 eV/Å and energy convergence of 10 -5 eV. A 520 eV plane wave cut off with a 5 × 5 × 5 k-mesh, centered at the Gamma point, is used to optimize the unit cell of LaNiO3. The Gaussian scheme for Brillouin zone integration is used with a smearing width of 0.1 eV. All our DFT calculations are carried out using the MedeA-VASP (Vienna ab initio simulation package) software [20]. For LaNiO3 we have calculated the optical