Charge Density Contour Research Articles

Investigations of structural, electronic and optical properties of YInO3 (Y = Rb, Cs, Fr) perovskite oxides using mBJ approximation for optoelectronic applications: A first principles study

The structural, electronic and optical properties of indium based novel combinations of ternary perovskite oxides YInO3 (Y = Rb, Cs, Fr) are investigated by first Principles DFT-based calculations scheme via Full Potential Linearly Augmented Plane Wave (FP-LAPW) technique. Comprehensive study is done among three cations (Rb, Cs, Fr) in the same order of symmetry in ABO3 cubical phase. Electronic properties are improved through PBE plus Tran and Blaha modified Becke-Johnson (PBE + TB-mBJ) functional. Using PBE-GGA, indirect band gaps are calculated to be 2.38 eV, 1.92 eV for RbInO3 and CsInO3, respectively. Whereas, FrInO3 exhibits direct band gap of 1.82 eV. However, these band gap values show improvement in all cases by the use of PBE + TB-mBJ functional. The phonon dispersion curves exhibit no imaginary phonon frequencies indicating that the studied compounds are structurally and dynamically stable. TDOS and PDOS results show the highest contribution of Fr-7s and In-5p states of FrInO3 in increasing conductivity. The electronic charge density contours depict covalent character between In ̶ O atoms. Whereas, spherical contours around the cations (Rb, Cs, Fr) show their ionic bonding. The optical analysis illustrates that the studied compounds possess conductivity and absorptivity in a wide range of the incident photon energies with their minimal reflectivity. The overall analyses depict that the considered compounds are potential candidates for applications in optoelectronic and other allied devices.

Electronic and optical behaviour of lanthanum doped CaTiO3 perovskite

To improve the efficiency of perovskite based solar cells, doping of heavier elements in Perovskite materials (ABX3) can modulate its electronic and optical properties significantly. Thus it is important to understand the possible microscopic origin of the band gap modification and optical enhancement after heavier element doping using first-principles studies. Here we investigate the effect of La doping, while substituting the Ca atom, on the electronic and optical properties in CaTiO3 perovskite material using generalized gradient approximation within density functional theory. We observe a decrease in lattice constants and bond lengths in LaxCa1−xTiO3, mainly due to re-distribution of electronic charge density between La and Oxygen, as confirmed by charge density contour. We further notice a widening of electronic band gap and an upward shift of Fermi level into the conduction band, thus characterizing LaxCa1−xTiO3 as an n-type material. DOS diagram attributes this shift mainly due to the appearance of La p-DOS and d-DOS and their repulsion with N p-DOS, when La enters into the host lattice at Ca site. Investigation of optical properties upon La Doping in CaTiO3 exhibits further shifting of polarization and refractive index to lower values as compared to its pure counterpart, due to dominating semiconducting behavior and hence one observes a blue shift in absorption and reflection spectrum accordingly. Energy loss function is found to be consistent with absorption and extinction coefficient measured in case of LaxCa1−xTiO3. All these results are found to be consistent with the existing experimental and first-principles studies.

Investigations of structural, electronic and optical properties of TM-GaO3 (TM = Sc, Ti, Ag) perovskite oxides for optoelectronic applications: a first principles study

We have examined structural, electronic and optical properties of TM-GaO3 (TM = Sc, Ti, Ag) perovskite oxides by means of first Principles study based on density functional theory (DFT). TM represents transition metal elements. To investigate structural properties, exchange correlation potential was determined by employing Full Potential Linearly Augmented Plane Wave (FP-LAPW) technique along with Perdew-Burke-Ernzerhof – GeneralizedGradient Approximation (PBE-GGA) functional. Moreover, Hubbard Ueff parameter LDA + U was used to overcome limitations of PBE-GGA functional. All compounds TM-GaO3 (TM = Sc, Ti, Ag) seem semi-conductor in nature because indirect band gap in each case has been observed with energies 1.33 eV, 0.75 eV and 1.95 eV, respectively. Partial density of states (PDOS) analyses portrayed that 3d orbitals of Sc & Ti, 4d orbital of Ag, and 2p orbital of anions contribute mainly to increase electronic conductivity of the studied compounds. Charge density contour plots depicted ionic nature of TM-cations, while, significant sharing of isolines between O and Ga atoms showed covalent character between them. These contours have also confirmed accumulation of charges around O atoms. Optical analysis revealed that the considered perovskite oxides show sharp increase in optical conductivity and absorptivity in higher energy range when energetic photons are incident upon. Remarkably, they displayed poor reflectivity. However, defect states introduced in the band gap region might be due to cations. These composites are suitable for photovoltaics and other optoelectronic applications

Influence of pressure on electro-mechanical properties of SrNbO3: A DFT study

In the enclosure of density functional theory along with GGA (generalized gradient approximation), incorporated in Wien2k code has been utilized to explore structural, electronic and mechanical properties of SrNbO3 (SNO). It has been found that spin-polarized phase of SNO is most stable at 60 GPa with the calculated lattice constant of 3.801 Å. The calculated lattice constant and bulk modulus at 0 GPa are found to be in agreement with literature. The present calculations predict that SNO is stable and antiferromagnetic in nature up to 60 GPa. The calculated charge density contours and Cauchy pressure depicts majority of the bonding nature between the content atoms of SNO is ionic with a small contribution of covalent bond. The band-gap is found traverse from indirect R-Г gap under 0 GPa to wider direct Г-Г gap under 60 GPa. Furthermore, calculated elastic constants, C11, C12 and C44 suggest that compound is stable up to 60 GPa and exhibits ductile, anisotropic nature. Beneficial electronic and mechanical applications are predicted for SNO that could be used in optoelectronic applications.

Generation of molybdenum hydride species via addition of molecular hydrogen across metal-oxygen bond at monolayer oxide/metal composite interface

Generation of molybdenum hydride species on monolayer oxide/metal composite via addition of molecular hydrogen across metal-oxygen bond is investigated for the first time utilizing periodic Van der Waals density-functional calculations. Lewis acid-base pair constructed by the interfacially defected oxide film and the metal support provides novel active sites for activating H2. The produced heterolytic dissociative state exhibits negative dissociative adsorption energy of −0.315 eV which thermodynamically facilitate the dissociation process of H2 on insulating oxide films. The penitential energy pathways are calculated to reveal the dynamics and reaction processes for H2 splitting at the oxide-metal interface. The differential charge density contour, electronic density plots, particular occupied orbitals, work function and electron localization function of H2 dissociation are interpreted to better understand the electronic properties of the unique dissociation behavior of H2 at interfacially defected magnesia. It is anticipated that the results here could help understand the mechanism of hydrogenation reactions on nanostructured oxide film and provide useful clue for enhancing the reactivity of insulating oxide toward activating H2.

Enlightening the stable ferromagnetic phase of SrAO3(A= Cr, Fe and Co) compounds using spin polarized quantum mechanical approach

This is an investigation of the atomic structure, opto-electronic and magnetic properties of SrAO3 (A = Cr, Fe and Co) compounds using first principles method. The ferromagnetic behavior is found the most stable phase for SAO. The calculated Goldschmidt's tolerance factor values predict that the studied compounds have a stable structure. Moreover, the calculated formation energy shows that SrAO3compounds are thermodynamically stable. The calculated density of states shows that the present compounds are metal and the direction of the magnetic moments of SrCrO3 is anti parallel to its spin. The charge density contours display a mixture of the covalent and ionic bonds between the content atoms of SrAO3 compounds. The optical parameters are calculated using the dielectric function real and imaginary parts. From the electronic and optical properties results, beneficial industrial applications can be expected for the present compounds.

A First Principle Study of Structural, Electronic, and Vibrational Properties of LuPdBi Half‐Heusler Alloy

Half‐Heusler alloys offer a variety of applications in the field of electronics and superconductors. They are suitable for the formation of thermoelectric materials and superconductors. Their stupendous applications arouse curiosity among many researchers. Therefore, in this paper, a systematic study of structural, electronic, and vibrational properties has been done using density functional theory and density functional perturbation theory. The structural properties such as lattice constant, bulk modulus, and pressure derivative of bulk modulus have been calculated. Electronic and bonding properties have been examined from electronic band structure, charge density contours, and Fermi surfaces. The phonon dispersion spectra and phonon density of states for LuPdBi are reported and discussed for the first time. Moreover, the eigenvector displacements for optical phonons at the zone center are also described to support the reliability of phonon calculations. The computation of phonon spectra disclosed the fact that the resulted phonons are real. Real frequencies of phonons are witness of alloy stability in the cubic phase. The superconducting properties have also been evaluated by employing electron–phonon interaction and Eliashberg theory. The Coulomb pseudopotential variable µ* is selected to be 0.11 and the computed value of transition temperature is found to be Tc = 1.802 K. This value of Tc is in agreement with the experimental value of Tc = 1.80 K.

Structure, electronic, magnetic and optical properties of cubic Hf1-x(TM)xO2 (X = 0, 0.25, TM = Mn, Fe, Co, Ni): A first principle investigation

In the present work the structural, electronic, optical and magnetic properties of pure cubic HfO2and 3d transition metal (Mn, Fe, Co, Ni) doped (Hf1-xTMxO2) alloys (x = 0.25%) have been investigated by Density Functional Theory (DFT) as implemented in the FP-LAPW (full-potential augmented plane wave plus local orbital's) method employing generalized gradient approximation (GGA) and TB-mBJ exchange correlation methods. The calculated results such as lattice parameters and band gap are in good agreement with available experimental results. The calculation indicates that Hf1-xTMxO2 with x = 0 is a symmetric band gap semi-conductor but as a result of 3d TM doping, the band structure changes dramatically, presenting the half-metallic nature for all Hf1-x(TM)xO2 (x = 0.25, TM = Mn, Fe, Co, Ni) with majority spin states (spin up) as metallic and minority spin states (spin down) as semi-conducting for TM = Mn, Fe, Co and for TM = Ni the majority spin states (spin up) as semi-conducting and minority spin states (spin down) as metallic. The main contributions to the magnetic moment are mainly from the doped transition metals,TM = Mn, Fe, Co and Ni atoms with partial moments of 3.67 μB, 4.08 μB, 2.36 μB and 2.16 μB, respectively. From the charge density contour plots it was found that Hf0.75TM0.25O2 compounds have merged ionic and covalent character for the Hf–O and TM–O bonds. Further we have also explored the optical properties like reflectivity, index of refraction, energy loss, optical spectrum (absorption spectrum) corresponding to the imaginary part of dielectric function in the range 0–30 eV.

Electrohydrodynamic formation of single and double emulsions for low interfacial tension multiphase systems within microfluidics

The feasibility of droplet formation from the dispersion of one viscous fluid within another immiscible viscous fluid with low interfacial tension is shown to be very limited. In this work, the process of emulsion formation for low interfacial tension multiphase systems (e.g. aqueous two-phase systems (ATPSs)) was simulated, where the liquids were exposed to an electric field within a microfluidic device. For the first time, the formation of double emulsion via electrohydrodynamic (EHD) force within microfluidics was investigated. A three dimensional (3D) numerical model was developed based on finite-volume discretization of the governing equations to simulate the EHD-based single and double emulsion formation for ATPSs within microfluidics. The dispersed viscous phase moving toward the active electrode is subjected to shear stress, producing instability on the two-phase interface and causing the formation of a necking area. Upon removal of the electric pulse, the dispersed phase moves in the opposite direction resulting in the formation of the droplet. The volume-of-fluid numerical method was applied to trace the two-phase interface, and a height function was imposed to deal with the 3D contact angles. The effect of capillary number and permittivity ratio of the phases on the size and shape of the droplets was assessed and compared with experimental data. Through controlling the interface between the phases, pressure contours, and volumetric charge density contours, it is possible to generate EHD-based single and double emulsions from viscous fluids within microfluidics with applications in drug delivery, tissue engineering and chemical and biological processes.

Spin Density for Intermetallic Compounds

We first performed a pure spin-polarized calculation on Nd2Fe14B using the self-consistent Full Potential Linearized Augmented Plane Wave (FPLAPW). The total charge density and the spin density calculated by taking the sum or the difference of spin-up and spin-down charge densities, respectively. In this paper, we present the spin and charge density contours for rare-earth transition metal compounds e.g. Nd2Fe14B in the (001) and (110) planes using spin-polarized only. The charge density map and the spin density map on the (001) and (110) plane of the tetragonal cell show the evidence for covalent bonding between Fe and B atoms.

Effects of doping of calcium atom(s) on structural, electronic and optical properties of binary strontium chalcogenides - A theoretical investigation using DFT based FP-LAPW methodology

The effects of doping of Ca atom(s) on structural, electronic and optical properties of binary strontium chalcogenide semiconductor compounds have been investigated theoretically using DFT based FP-LAPW approach by modeling the rock-salt (B1) ternary alloys CaxSr1−xS, CaxSr1−xSe and CaxSr1−xTe at some specific concentrations 0 ≤ x ≤ 1 and studying their aforesaid properties. The exchange-correlation potentials for their structural properties have been computed using the Wu-Cohen generalized-gradient approximation (WC-GGA) scheme, while those for the electronic and optical properties have been computed using recently developed Tran-Blaha modified Becke-Johnson (TB-mBJ) scheme. In addition, we have computed the electronic and optical properties with the traditional BLYP and PBE-GGA schemes for comparison. The atomic and orbital origin of different electronic states in the band structure of each of the compounds have been identified from the respective density of states (DOS). Using the approach of Zunger and co-workers, the microscopic origin of band gap bowing has been discussed in term of volume deformation, charge exchange and structural relaxation. Bonding characteristics among the constituent atoms of each of the specimens have been discussed from their charge density contour plots. Optical properties of the binary compounds and ternary alloys have been investigated theoretically in terms of their respective dielectric function, refractive index, normal incidence reflectivity and optical conductivity. Several calculated results have been compared with available experimental and other theoretical data.

Effects of barium (Ba) doping on structural, electronic and optical properties of binary strontium chalcogenide semiconductor compounds - A theoretical investigation using DFT based FP-LAPW approach

The effects of doping of Ba atom(s) on structural, electronic and optical properties of binary strontium chalcogenide semiconductor compounds have been investigated theoretically using DFT based FP-LAPW approach by modeling the rock-salt (B1) ternary alloys BaxSr1−xS, BaxSr1−xSe and BaxSr1−xTe at some specific concentrations x = 0.0, 0.25, 0.50, 0.75 and 1.0 and studying their aforesaid properties. The exchange-correlation potentials for their structural properties have been computed using the Wu-Cohen generalized-gradient approximation (WC-GGA) scheme, while those for the electronic and optical properties have been computed using the WC-GGA and Tran-Blaha modified Becke-Johnson (TB-mBJ) scheme. The thermodynamic stability of all the modeled ternary alloys have been investigated by calculating their respective enthalpy of formation. The atomic and orbital origin of different electronic states in the band structure of each of the compounds have been identified from the respective density of states (DOS). Using the approach of Zunger and co-workers, the microscopic origin of band gap bowing has been discussed in term of volume deformation, charge exchange and structural relaxation. Bonding characteristics among the constituent atoms of each of the specimens have been discussed from their charge density contour plots. Optical properties of the binary compounds and ternary alloys have been investigated theoretically in terms of their respective dielectric function, refractive index, normal incidence reflectivity and optical conductivity. Several calculated results have been compared with available experimental and other theoretical data.

Theoretical investigation of structural, electronic and optical properties of MgxBa1−xS, MgxBa1−xSe and MgxBa1−xTe ternary alloys using DFT based FP-LAPW approach

Density functional theory (DFT) based full-potential linearized augmented plane wave (FP-LAPW) methodology has been employed to investigate theoretically the structural, electronic and optical properties of MgxBa1−xS, MgxBa1−xSe and MgxBa1−xTe ternary alloys for 0 ≤ x ≤ 1 in their rock-salt (B1) crystallographic phase. The exchange-correlation potentials for the structural properties have been computed using the Wu-Cohen generalized-gradient approximation (WC-GGA) scheme, while those for the electronic and optical properties have been computed using both the WC-GGA and the recently developed Tran-Blaha modified Becke-Johnson (TB-mBJ) schemes. The thermodynamic stability of all the ternary alloys have been investigated by calculating their respective enthalpy of formation. The atomic and orbital origin of different electronic states in the band structure of the compounds have been identified from the respective density of states (DOS). Using the approach of Zunger and co-workers, the microscopic origin of band gap bowing has been discussed in term of volume deformation, charge exchange and structural relaxation. Bonding characteristics among the constituent atoms of each of the specimens have been discussed from their charge density contour plots. Optical properties of the binary compounds and ternary alloys have been investigated theoretically in terms of their respective dielectric function, refractive index, normal incidence reflectivity and optical conductivity. Several calculated results have been compared with available experimental and other theoretical data.

DFT based FP-LAPW investigation of structural, electronic and optical properties of SrxPb1−xS, SrxPb1−xSe and SrxPb1−xTe ternary alloys

The structural, electronic and optical properties of SrxPb1−xS, SrxPb1−xSe and SrxPb1−xTe semiconductor ternary alloys for 0 ≤ x≤ 1 in their rock-salt (B1) crystallographic phase have been calculated using the full-potential linearized augmented plane wave (FP-LAPW) method under the framework of density functional theory (DFT). Using the Wu-Cohen generalized-gradient approximation (WC-GGA) induced exchange-correlation potential scheme, the ground state structural parameters have been calculated. Electronic properties of the binary compounds and their ternary alloys have been calculated mainly using Tran-Blaha modified Becke-Johnson (TB-mBJ) parameterization scheme. The atomic and orbital origin of different electronic states in the band structure of each of the compounds have been identified from their respective density of states (DOS). Using the approach of Zunger and co-workers, the microscopic origin of band gap bowing has been discussed in term of volume deformation, charge exchange and structural relaxation. Bonding characteristics among the constituent atoms of each of the specimens have been discussed from their charge density contour plots. Optical properties of the binary compounds and their ternary alloys have been calculated in terms of their respective dielectric function, refractive index, reflectivity and optical conductivity. Some calculated results are compared with available experimental and other theoretical results.

Atomic, electronic, and magnetic properties of bimetallic ZrCo clusters: A first-principles study

Here, we report the atomic, electronic, and magnetic structures of small ZrmCon (m + n = 2, 4, 6, and 8) alloy clusters based on spin-polarized density functional theory under the plane wave based pseudo-potential approach. The ground state geometry and other low-lying stable isomers of each cluster have been identified using the cascade genetic algorithm scheme. On the basis of the relative energy, it is found that Zr2Co2 (for tetramer), Zr3Co3 (for hexamer), and Zr4Co4 (for octamer) are the most stable isomers than others. In order to underscore the hydrogen storage capacity of these small clusters, the hydrogen adsorption on the stable ZrmCon (m + n = 2, 4, 6, and 8) clusters has also been studied. The electronic structures of ZrmCon clusters with and without adsorbed hydrogen are described in terms of density of states spectra and charge density contours.

Half-Metallic Ferromagnetism in Li6VCl8, Li6MnCl8, Li6CoCl8 and Li6FeCl8 from First Principles

Within the framework of density functional theory, the electronic structure and magnetic properties have been studied for the Li6XCl8 (X = V, Mn, Co and Fe) Suzuki-type compounds. Features such as the lattice constant and the bulk modulus and its pressure derivative are reported. The Li6XCl8 (X = V, Mn, Co and Fe) Suzuki-type compounds show half-metallic ferromagnetism with total magnetic moments (Mtot) of 3, 5, 3, and 4 μB per formula unit, respectively. The half metallicity is originated by the hybridization of TM-d states with Cl-p states. The analysis of charge density contours leads us to conclude that the bonding character in these compounds is a mixture between covalent and ionic natures. The half-metallic nature and complete 100 % spin polarization show that the new compounds have a potential application in spintronic devices.

Investigations of mechanical, electronic, and magnetic properties of non-magnetic MgTe and ferro-magnetic Mg0.75TM0.25Te (TM = Fe, Co, Ni): An ab-initio calculation

The mechanical, electronic and magnetic properties of non-magnetic MgTe and ferro-magnetic (FM) Mg0.75TM0.25Te (TM = Fe, Co, Ni) in the zinc-blende phase are studied by ab-initio calculations for the first time. We use the generalized gradient approximation functional for computing the structural stability, and mechanical properties, while the modified Becke and Johnson local (spin) density approximation (mBJLDA) is utilized for determining the electronic and magnetic properties. By comparing the energies of non-magnetic and FM calculations, we find that the compounds are stable in the FM phase, which is confirmed by their structural stabilities in terms of enthalpy of formation. Detailed descriptions of elastic properties of Mg0.75TM0.25Te alloys in the FM phase are also presented. For electronic properties, the spin-polarized electronic band structures and density of states are computed, showing that these compounds are direct bandgap materials with strong hybridizations of TM 3d states and Te p states. Further, the ferromagnetism is discussed in terms of the Zener free electron model, RKKY model and double exchange model. The charge density contours in the (110) plane are calculated to study bonding properties. The spin exchange splitting and crystal field splitting energies are also calculated. The distribution of electron spin density is employed in computing the magnetic moments appearing at the magnetic sites (Fe, Co, Ni), as well as at the non-magnetic sites (Mg, Te). It is found that the p–d hybridization causes not only magnetic moments on the magnetic sites but also induces negligibly small magnetic moments at the non-magnetic sites.

Theoretical Investigation of Structural, Electronic, and Mechanical Properties of Two Dimensional C, Si, Ge, Sn

In this article, we investigate the predictions of the first principles on structural stability, electronic and mechanical properties of 2D nanostructures: graphene, silicene, germanene and stenane. The electronic band structure and density of states in all these 2D materials are found to be generic in nature. A small band gap is generated in all the reported materials other than graphene. The linearity at the Dirac cone changes to quadratic, from graphene to stenane and a perfect semimetalicity is exhibited only by graphene. All other 2D structures tend to become semiconductors with an infinitesimal band gap. Bonding characteristics are revealed by density of states histogram, charge density contour, and Mulliken population analysis. Among all 2D materials graphene exhibits exotic mechanical properties. Analysis by born stability criteria and the calculation of formation enthalpies envisages the structural stability of all the structures in the 2D form. The calculated second order elastic stiffness tensor is used to determine the moduli of elasticity in turn to explore the mechanical properties of all these structures for the prolific use in engineering science. Graphene is found to be the strongest material but brittle in nature. Germanene and stenane exhibit ductile nature and hence could be easily incorporated with the existing technology in the semiconductor industry on substrates.

First-principles study of the structural and electronic properties of ultrathin silver nanowires

By using first-principles calculations based on density-functional theory, we have systematically investigated the equilibrium structure, stability and electronic properties of silver nanowires (AgNWs) with dimer, triangular, square, pentagonal and hexagonal cross-section. It is found that, using the string tension criterion, for the triangular and square AgNWs with small diameters the preferred structures should be the hollow one with staggered configuration, while for the pentagonal and hexagonal AgNWs with bigger diameters the preferred structures should be the staggered ones which contain a linear chain along the wire axis passes through the center of the polygons, where each chain atom is just located at a point equidistant from the planes of polygons. Electronic band structures and density of states calculations show that the AgNWs with different structures exhibit metallic behavior. Charge density contours show that there is an enhanced interatomic interaction in AgNWs compared with Ag bulk.

DFT and modified Becke Johnson (mBJ) potential investigations of the optoelectronic properties of SnGa4Q7 (Q = S, Se) compounds: Transparent materials for large energy conversion

Electronic structure and optical properties of SnGa4Q7 (Q = S, Se) compounds were investigated using a full potential linearized augmented plane wave method based on density functional formalism. Electronic band structures show an indirect semiconducting wide band gap two different approaches (EV-GGA and mBJ). The band gap values are estimated at 2.90 (2.25 eV) and 3.11 (2.49 eV) for EV-GGA and mBJ for SnGa4S7 (SnGa4Se7), respectively. Densities of states show that Sn-5s and S/Se-3p/4p states are dominating the region around Fermi level form valence band maximum and conduction band minimum. The computed electronic charge density contours demonstrate that SnGa4Q7 (Q = S, Se) show a mixture between ionic and covalent characters. Optical parameters including the dielectric constant, absorption coefficient, reflectivity, refractive index, energy loss function, and birefringence are also reported to investigate the potential role of SnGa4Q7 (Q = S, Se) compounds for solar energy conversion application.