Re: Ab-initio study of electronic and Structural properties for BaSnO 3 Compound using DFT calculations and FP-LAPW Technique in wein2k Software

(Perovskites Photovoltaic) PPV cells are the hottest topics in solar cells in the recent years, because of the remarkable structural and electronic properties and hence rapid progress in material science. The Challenge associated with high-mobility BaSnO 3 films is to grow. It shows high carrier mobility and UV-visible transparency has been attracting more and more attention as a very promising component for the next generation opto-electronics. Here, we demonstrate a Structural and Electronics properties (Sp and Ep), To characterize this compound theoretical calculation have been performed by using first principal method and the results show BaSnO 3 is conductor at 0eV i.e. room temperature and gaining energy make more conduction transferring more electrons from conduction to valence bands. BaSnO 3 shows 5.78e.v maximum for the conduction. We have studied this compound in ideal cubic phase. At 0° Kelvin calculation are performed to get different properties. No experimental studies have been done on this compound. And it was difficult to accumulate its experimental data. WC-GGA is used for the study of structural properties of BaSnO 3. This Correlation potential can also be used for the calculation of the various perovskite. Depending on the cubic (ABX3) composition, perovskites exhibit a wide range of structural and electronic properties, which are optimized for different applications.


Introduction
High-mobility of the perovskite BaSnO3 films are of significant interest as new wide bandgap semi-conductors for the power electron as a new transparent conducting oxide and as a wide bandgap semiconductor for power electronics. To characterize this compound theoretical calculation have been performed by using first principal method and the results show BaSnO3 is conductor at 0eV i.e. Perovskites belongs to oxide family which has studied yet. They show many important and interesting most properties. Perovskites exhibit polarization if we apply electric field. The basic purposes of this thesis are "The first

Stability Conditions of All Perovskites
The conditions required for a stable perovskite is: i. Valance bond should be balanced.
ii. Ionic radii must fulfill the condition of Goldschmidt's criteria Goldschmidt perform great work on the study of perovskites, He determine the tolerance factor for perovskites. [1, 2]  These compounds are stable in nature perovskite general structure is cubic but in actual it occurs at pseudo cubic [3]. at the corner there is atom A and at the center there is atom B and Atom X is at the face center of cube.

My Perovskites Compounds
By using general formula of ABX3, My perovskites compound on which my searching is continuous, is Barium Tin Oxide or also known as Barium titanite.

BaSnO3
It is a semiconducting oxide with wide band gap of 3.1 eV. Recently, it is discovered that BaSnO3 doped with few percent of Lanthanum exhibits unusually high electrical mobility [5], at room temperature and superior thermal stability at high temperatures [6].
It has a very low dielectric response (range from 4.9-6.6). This oxide is stable against zone center phonons in cubic perovskite structure as well as KTaO3 and BaZro3 also same oxides as Barium tin oxides.

Barium (Ba)
It was found by S.H. Davy in England in 1808. It is named after Greek word "Barys" which means heavy. Symbolically it is represented by Ba. It is s-block element and a member of period 6 with atomic number 56. It is fifth element of group two. It is alkaline earth metal which is very reactive. It is metallic element which exist is soft solid and it is silvery white like lead in pure form. It is good electrical conductor. [7] It easily reacts with water and alcohol. In glasses and paints small proportions of barium elements are added.
Barium in salt form also used in flames to change the color to green. It has body centered cube crystal structure [7].  In ancient times conversion of other metal into gold was done by Tin which is knows as Alchemy [6,8]. Its crystal structure is existing into two forms that is cubic and tetragonal known as alpha-tin and beta-tin. It is used in marine environments because it is fungicide and bactericide. Usually it is silvery white metal with highly crystalline structure.

Figure (1.3.2): An ore of Tin
It is p-block element in fifth period of periodic  [8,9].

Some Parameters, Ba, Sn, and O
The values of different parameters related with different assets are given as :

Tolerance Factor
It was determined in 1926 by Victor. M Goldschmidt. Tolerance factor was introduced to measure the distortion in perovskites from their ideal cubic structure. There is great importance of Cationic and Anionic radii of atoms in perovskite compound which plays an important role in the alteration of ideal cubic structure [11]. The deviation of orthogonal, rhombohedral can be determined by using of G. schmidt tolerance factor is given as: where and are the ionic radii of the cations and is the ionic radii of anion [12]. For the ideal cubic perovskites values of the tolerance factor should be equal to 1. But in the case of the distorted perovskites that value changed from 1. Equation 1.1 describes that sum of ionic radii is nearly equal to the bond length [13].Tolerance factor for the different structure is shown in table 1.3.

Some Applications of Perovskites
Due to some remarkable physical, chemical and structural properties, they have an important place in the world of science research. These multi purposes causes many applications of the perovskites and thus have an important place in the Industry field. A perovskites oxide Barium titrate have so much variety of applications because of ionic and mixed conductivity it is used as capacitors, thermistors, temperature co-efficient, and piezoelectric devices (in which device produces AC voltage when we apply mechanical stress) etc [13]. perovskites that are used in highly effective photovoltaic are synthetic perovskites [15]. They are prepared same as solar cell by method of thin film [14]. They are also used to produced Laser light, when LiAlO3 is doped with neoydium they produce laser light of 1080nm. Those perovskites have high resistivity are used in dielectric material, some of them are LaTiO3, LaVO3, etc. and some of them are good conductor because B atom in ABO3 having oxidization state of +2 [16]. They are also used in oxygen sensor like SrTiO3.

Introduction to Density Functional Theory
To understand the internal forces of the atoms when they join in the solids and to study the A simple glance on the background in table is given as:

Execution of DFT
In an external potential of atomic nuclei Density Functional Theory is the most successful theory of today science and used for the study of the properties of system of electrons. The major advantage of the Density Functional Theory is reduction 3N degree of freedom of a system to three degree of freedom that made Density Functional Theory able to solve complicated system [20]. It gives ground state properties of material which further used to understand the behavior of that material with other materials, in general it gives the theoretical approach to the physical properties as well as electronic, optical, thermal, magnetic and electrostatic properties on the ground state level [21]. In respect to the Chemistry approach Density Functional Theory is also a successful theory, in which it has many applications.
has direct relation of ground state energy of the system with its electron density.
This electron density is actually main variable on which whole Density Functional Theory exists [21,22].

Boundaries of DFT
DFT cannot be useful to determine each and every properties and has deficiencies in determining some properties listed below: Absolute values of band gap cannot be determine.

 Superconductivity
Accurate prediction is not available in DFT.
 High temperature properties.
Unable to calculate the properties at higher temperature close to melting points[19, 21,22].

Introduction to Wien2k
To calculate electronic, structural, magnetic, thermal, optical and many others properties of the materials in SSP in which we use the concepts of density functional theory these all can be measured in single package called Wien2k software. One of the most and accurate methods of full potential is linearized augmented plane wave method (LAPW), which is used to calculate band structures and it is the base of the wien2k package. Wien2k deals with the electrons and their relativistic effects and many others features like quantum mechanical properties.

Compatibility
Wien2k is a computer program having FORTRAN90 language, which require UNIX operating system, and the installation in which program are connected through C-Shell script.
Following are the computers systems on which Wien2k can be run successfully.

Working
We are dealing our compounds in ideal conditions in material science and in ideal crystals.
We consider the crystal at 0°k temperature, thus we can calculate many properties at ground state level. Like every software we use exchange correlation potential in Wien2k also [1, 23,24].

Wien2k Application
To understand the structure and many properties of an atom or compound it has many applications in the field of Science.
 It is used to solve Kohn-Sham Equation of DFT.
 For the calculation of structural properties.

Software codes
It consists of many independent FORTRAN90 programs, which are linked to each other's through C-shell script. This software can be executed using any web browser or w2web interface. We used wien2k software by using short commands. The main steps for the software are;  Define structure.
 Initialize all commands.
 SCF (run self-consistent-field These are the basic building block for the run to this software [26].

Structure Generation
First, we need to generate structure of the compound to find out the properties of the compound. We need to click on the struct-gen command and then put all the values of the compound like position of each atom, number of atoms, lattice constant, angels of atoms, and space group. By entering all commands, we have to click on Save structure, after that RMT is automatically set, by continuing editing structure file is saved [3].

View Structure
After input all data of the given compound and executing then click on the View_struct to view the structure of the compound.

Initialize the Calculation
After saving the structure, now we are going to initialize the calculations for properties with symmetry. Init_lapw term is used to initialize the command, initialization depends upon the 6 properties, these properties perform different task.

 X-nn
In this term 'nn' stands for nearest neighbor distance, this is used to calculate the distance between spheres and for checking the overlapping of all atomic spheres.

 X-sgroup
It specifies the space group and point group of the non-equivalent atoms. It can also distinguish the different atoms by using value of the Z uniquely. It can find out the smallest unit cell and also shift the origin of a unit cell.

 X-symmetry
Space group symmetry is checked by the 'X-symmetry' command. This program gives the atomic densities of the compound.

 X-lstart
It is also called LSDA programing it is start by Hartree units at input and end on Rydberg units at output. This program can also produce atomic potential.

 X-kgen
This produce k-mesh by converging all the k points in an irreducible region of the brillouin zone.

 X-dstart
To make initial density of crystalline solids calculation from x-lstart is superimposed. This program is called ''superposition of the Atomic Density''. [27]

Volume Optimization Curve
To find out shape and size of the unit cell having total energy optimization process is used.
Shape and size are very important parameters. We use experimental values as a input, to calculate the total energy of the perovskites compound this can be measured by the use of Murnaghan Equation.

E(v) = E˳(v) + BV/ B́ (B́ -1) [ B { 1 -V˳/ V } + (v˳ / v) B́ -1 (3.1)
In equation (  Thus, we can calculate energy by entering the values of volume [28]. Therefore, its graph is always parabola along y-axis. The graph is plotted between V and E . This process is known as Volume optimization, the lattice constant is also determined from the equilibrium volume. The range of the graph tells us how much time is required to give volume optimization [29].

Evaluation of Properties
After SCF cycle, the properties of the given compound is obtained and calculated, like, electronic, optical, etc. can be obtained using wien2k software. since, we know the properties of the material or compound, we can use these into the field of science [30].

General Behavior of BaSnO3
In order to characterize this compound theoretical calculation have been performed by using first principle method. I have studied this compound in ideal cubic phase. At 0° Kelvin calculation are performed in order to get different properties. No experimental studies have been done on this compound. And it was difficult to accumulate its experimental data.
BaSnO3 having space group 221_pm3m. Barium Stannate (BaSnO3) depending on temperature it have different types of structures. It shows many dramatic properties for example ionic conductivity, superconductivity, colossal magnetoresistance [30][31][32], as well as ferromagnetism and ferroelectricity and semi-conductivity70. It also shows piezoelectric and optical properties which have great importance in microelectronics and telecommunications respectively [21,32].
In this chapter I will study structural and electrical properties of BaSnO3 along with graphs in WEIN2k software.

Structural Properties of BaSnO3.
WC-GGA is used for the study of structural properties of both BaSnO3 . This Correlation potential can also be used for the calculation of the various perovskites. It is comparatively most accurate technique having less uncertainty. For the very first compound the orientation is adjusted in such a way that Ba is placed at origin and location of Atom in compound is (0,0,0), and for Sn it is in the center of the cubic structure with location (1/2,1/2,1/2), and for the last atom oxygen is in the face centered having location (½,½,0), (1/2,0,1/2), and (0,1/2,1/2). For the structural properties of BaSnO3 it needs input parameters like, lattice constant, space group, and atomic positions of the every atom etc. These parameters are given as below in table.

Optimization Curve BaSnO3
In case of BaSnO3, the increase in volume of the unit the values of the energy decreases of the crystal structure. The certain value of the volume which is minimum energy of the volume, after this value energy of the volume increases, this is called optimized equilibrium energy, because the system is in the equilibrium.   In the Graph shows different orbitals [28]. Valence electrons are nearly very close to the conduction's electrons, when they jump from one band to another attain some energy as photons, and hence peaks show only for the valence electrons in the DOS.

Electrons Density
The measure of the probability of the electrons around the atom is called electron density,  The very first graph is for the BaSnO3 in which symmetric is shown for the electrons density when magnetic field is absence, the main center portion shows combine effect of Ba-Sn, the light green color is for the oxygen representation, the upper corner shows Ba-O interactions and Sn-O shows lower corner interaction [21,31,32].

Band Gap
It can be defined as: The energy of the states in which the electrons are found or exits are called Energy bands or Allowed Gap. On the other hand, those energy states in which the electrons cannot be exists are called Forbidden Gaps or Electronic Band Gaps [28].
The graph for the band structure for the BaSnO3 is also studies by use of the Wien2k package are  Wide bandgap perovskite oxides with high room temperature conductivities and structural compatibility with a diverse family of organic/inorganic perovskite materials are of significant interest as transparent conductors and as active components in power electronics. Such materials must also possess high room temperature mobility to minimize power consumption and to enable high-frequency applications. Acknowledgements: