Elastic and optical properties of BeS,BeSe and BeTe under pressure

We have performed the first principles full-potential linearized augmented plane wave calculations (FP-LAPW) with density functional theory in local density approximations (LDA), in aim to determine and to predict the pressure dependence of structural and optical properties of zinc-blende BeS, BeSe and BeTe compounds. The elastic constant, refractive index and its variation with hydrostatic pressure are well described.     

Electronic structure and magnetic properties of the perovskite cerium manganese oxide from ab initio calculations

We have performed first-principle calculations of the structural, electronic and magnetic properties of cerium manganese oxide (CeMnO)₃, using full-potential linearized augmented plane-wave (FP-LAPW) scheme within GGA and GGA+U approaches. Features such as the lattice constant, bulk modulus and its pressure derivative are reported. Also, we have presented our results of the band structure and the density of states. The results show a half-metallic ferromagnetic ground state for CeMnO₃ in GGA+U treatment, whereas semi-metallic ferromagnetic character is observed in GGA. The results obtained, make the cubic CeMnO₃ a candidate material for future spintronic application.     

First principle study of spintronic properties for double perovskites Ba2XMoO6 with X=V,Cr and Mn

Cubic double perovskites Ba₂XMoO₆ (X=V, Cr and Mn) compounds are studied using the full potential linearized augmented plane wave (FP-LAPW) method within the frame work of density functional theory (DFT). The structural, electronic and magnetic properties are calculated by using the Generalized Gradient Approximation (GGA), GGA+U and modified Becke–Johnson mBJ-GGA. Density of States and band structure results reveal a similar half-metallic ferromagnetic ground state for Ba₂CrMoO₆. Whereas, a metallic ferromagnetic character is predicted for Ba₂VMoO₆ and a matching metallic ferromagnetic ground state is obtained for Ba₂MnMoO₆. The mBJ calculations yield a better energy-gap than the GGA and GGA+U methods.     

A density functional study of structural,electronic and optical properties of titanium dioxide: Characterization of rutile,anatase and brookite polymorphs

Study of fundamental physical properties of titanium dioxide (TiO₂) is crucial to determine its potential for different applications, such as study of electronic band gap energy is essential to exploit it for optoelectronics and solar cell technology. We present here investigations pertaining to structural, electronic and optical properties of rutile, anatase and brookite polymorphs of TiO₂ by employing state of the art full potential (FP) linearized (L) augmented plane wave plus local orbitals (APW+lo) approach realized in WIEN2k package and framed within density functional theory (DFT). To incorporate exchange correlation(XC) energy functional/potential part into total energy, these calculations were carried out at the level of PW–LDA, PBE–GGA, WC–GGA, EV–GGA, and mBJ–GGA which are exploited as the manipulated variables in this work. From our computations, the obtained structural parameters results were found to be consistent with the available experimental results. The analysis of electronic band gap structure calculations point to TiO₂ as a semiconducting material in all three phases, whereas band gap character around Fermi level was found to be indirect for anatase, and direct for rutile and brookite phases. Density of state (DOS) profiles showed a substantial degree of hybridation between O 2p and Ti 3d in conduction and valence band regions, illustrating a strong interaction between Ti and O atoms in TiO₂ compund. In addition, our investigations of the optical properties also endorse the interband transitions from O 2p in valence band to Ti 3d in conduction band.     

First principles study of the electronic structures and magnetic properties of transition metal-doped cubic indium nitride

First principles density functional calculations, using a full potential linearized augmented plane wave (FP-LAPW) method in local spin density approximation(LSDA), have been performed in order to investigate the structural, electronic and magnetic properties of In_1−xTM_xN(TM=Cr,Fe,Mn,V) in zinc-blende phase. Dependence of structural parameter values on the composition x have been analyzed in the x=0.25, x=0.50, and x=0.75, we found the existence of deviation from Vegard׳s law. Calculated electronic structure and the density of states of these alloys are discussed in terms of the contribution of TM 3d, N 2p, and In 3d states. The magnetic moment of In_1−xTM_xN has been studied by increasing the concentration of TM atom. The contribution of TM atom is the most important source of the total magnetic moment in these alloys, while it is minor in In and N.     

Simulated solar cell device of CuGaSe2 by using CdS,ZnS and ZnSe buffer layers

We have performed ab-initio calculations for the structural, electronic, optical, elastic and thermal properties of the copper gallium chalcopyrite (CuGaSe₂). The Full Potential Linearized Augmented Plane Wave (FP-LAPW) method is used to find the equilibrium structural parameters and to compute the full elastic tensors. We have reported electronic and optical properties with the recently developed density functional of Tran and Blaha. Furthermore, optical features such as dielectric functions, refractive indices, extinction coefficient, optical reflectivity, absorption coefficients, optical conductivities, are calculated for photon energies up to 30 eV. The thermodynamical properties such as thermal expansion, heat capacity, Debye temperature, entropy and Grüneisen parameter, bulk modulus and hardness are calculated employing the quasi-harmonic Debye model at different temperatures (0–1200 K) and pressures (0–8 GPa) and the silent results are interpreted. To check the potentiality of CuGaSe₂ as future solar cell material, device modeling and simulation studies have been carried out with a variety of buffer layers over CuGaSe₂ absorption layer. The band diagram and J/V curves are analyzed and device performance parameters i.e. efficiency, open circuit voltage, short circuit current, quantum efficiency are calculated for CdS, ZnS and ZnSe buffer layers. Simulation results for CuGaSe₂ thin layer solar cell show the maximum efficiency (15.8%) with ZnSe as the buffer layer. Most of the investigated parameters are reported for the first time.     

Thickness‐Dependent Structural Evolutions and Growth Models in Relation to Carrier Transport Properties in Polycrystalline Pentacene Thin Films

Thickness‐dependent crystal structure, surface morphology, surface energy, and molecular structure and microstructure of a series of polycrystalline pentacene films with different film thickness ranging from several monolayers to the several hundred nanometers have been investigated using X‐ray diffraction (XRD), atomic force microscopy (AFM), contact angle meter, and Raman spectroscopy. XRD studies indicate that thin film polymorphs transformation behaviours are from the orthorhombic phase to the thin‐film phase and then to the triclinic bulk phase as measured by the increased tilt angle (θ_tilt) of the pentacene molecule from the c‐axis toward the a‐axis. We propose a growth model that rationalizes the θ_tilt increased along with increasing film thickness in terms of grain size and surface energy varying with film growth using AFM combined with contact angle measurements. The vibrational characterizations of pentacene molecules in different thickness films were investigated by Raman spectroscopy compared to density functional theory calculations of an isolated molecule. In combination with XRD and AFM the method enables us to distinguish the molecular microstructures in different thin film polymorphs. We proposed a methodology to probe the microscopic parameters determining the carrier transport properties based on Davydov splitting and the characteristics of aromatic C–C stretching modes in Raman spectra. When compared to the triclinic bulk phase at a high thickness, we suggest that the first few monolayer structures located at the dielectric surface could have inferior carrier transport properties due to weak intermolecular interactions, large molecular relaxation energy, and more grain boundaries.     

Electronic and Optical Modeling of Solar Cell Compounds CuGaSe<Subscript>2</Subscript> and CuInSe<Subscript>2</Subscript>

We present dielectric-function-related optical properties such as absorption coefficient, refractive index, and reflectivity of the semiconducting chalcopyrites CuGaSe₂ and CuInSe₂. The optical properties were calculated in the framework of density functional theory (DFT) using linear combination of atomic orbitals (LCAO) and full-potential linearized augmented plane wave (FP-LAPW) methods. The calculated spectral dependence of complex dielectric functions is interpreted in terms of interband transitions within energy bands of both chalcopyrites; for example, the lowest energy peak in the e₂ (w) \varepsilon_{2} (\omega ) spectra for CuGaSe₂ corresponds to interband transitions from Ga/Se-4p → Ga-4s while that for CuInSe₂ emerges as due to transition between Se-4p → In-5s bands. The calculated dielectric constant, e₁ (0) \varepsilon_{1} (0) , for CuInSe₂ is higher than that of CuGaSe₂. The electronic structure of both compounds is reasonably interpreted by the LCAO (DFT) method. The optical properties computed using the FP-LAPW model (with scissor correction) are close to the spectroscopic ellipsometry data available in the literature.     

First-principles investigations of structural,electronic and magnetic properties of cubic LaMnO3

Using first-principle density functional calculations, the structural, electronic and magnetic properties of cubic perovskite LaMnO₃ were studied by means of the full-potential linear muffin-tin orbital method. Calculations were performed within the local spin density approximation (LSDA) to the exchange correlation potential. The magnetic phase stability was determined from the total energy calculations for both ferromagnetic (FM) and non-magnetic (NM) phases. Our calculations show that the magnetic phase is more stable than the non-magnetic phase. To our knowledge the elastic constants of this compound have not yet been measured or calculated, hence our results serve as a first quantitative theoretical prediction for future study. Additionally, the band structure, the density of state and the magnetic moments were analyzed.     

Electronic band structure and optoelectronic properties of double perovskite Sr2MgMoO6 through modified Becke-Johnson potential

The crystal structure, electronic and optical properties of double perovskite Sr₂MgMoO₆ have been calculated by using the full-potential linear augmented plane wave (FP-LAPW) method. The band structure and density of states (DOS) were carried out by the modified Becke–Johnson (mBJ) exchange potential approximation based on the density functional theory (DFT). The calculated band structure shows a direct band gap (Γ–Γ) of 2.663 eV for Sr₂MgMoO₆. The compound Sr₂MgMoO₆ has a triclinic structure with the space group I-1, the lattice parameters a=5.5666 Å, b=5.5661 Å and c=7.9191 Å, which are used in our calculations. The optical parameters, like dielectric constant, refractive index, reflectivity and energy loss function were also calculated and analyzed. This work provides the first quantitative theoretical prediction of the optical properties and electronic structure for the triclinic phase of Sr₂MgMoO₆.     

First-principle study of structural,electronic and magnetic properties of chromium-doped magnesium selenide: An interesting demonstration of half-metallic ferromagnetism

The structural, electronic and magnetic properties of Cr-based MgSe in zinc blende phase have been investigated by employing the full-potential linear augmented plane waves plus local orbitals (FP-LAPW+lo) method within the spin-polarized density functional theory (DFT). According to our findings, Mg_1−xCr_xSe exhibits a half-metallic characteristic, where the ferromagnetic state is more favorable than the antiferromagnetic state. The band structure results of half-metallic Mg_1−xCr_xSe system for x=0.25, 0.50 and 0.75 show 100% spin-polarization at the Fermi level (E_F). The total magnetic moment is 4 μ_B which is mainly due to the Cr-3d states at the Fermi level (E_F). Our results indicate the presence of small magnetic moments arising from the other non-magnetic atoms as well. We also calculated the spin dependent charge densities to understand the bonding nature of the system.     

Novel Polymorph of GaSe

2D GaSe is a semiconductor belonging to the group of post-transition metal chalcogenides with great potential for advanced optoelectronic applications. The weak interlayer interaction in multilayer 2D materials allows the formation of several polymorphs. Here, the first structural observation of a new GaSe polymorph is reported, characterized by a distinct atomic configuration with a centrosymmetric monolayer (D_3d point group). The atomic structure of this new GaSe polymorph is determined by aberration-corrected scanning transmission electron microscopy. Density-functional theory calculations verify the structural stability of this polymorph. Furthermore, the band structure and Raman intensities are calculated, predicting slight differences to the currently known polymorphs. In addition, the occurrence of layer rotations, interlayer relative orientations, as well as translation shear faults is discussed. The experimental confirmation of the new GaSe polymorph indicates the importance of investigating changes in the crystal structure, which can further impact the properties of this family of compounds.     

Structural, electrical and optical properties of GZO/HfO2/GZO transparent MIM capacitors

Metal–insulator–metal (MIM) transparent capacitors were prepared by pulsed laser deposition (PLD) on glass substrates. The effect of the thickness of the dielectric layer and oxygen pressure on structural, electrical, and optical properties of these capacitors was investigated. Experimental results show that film thickness and oxygen pressure have no effect on the structural properties. It is also found that the optical properties of the HfO₂ thin films depend strongly on both the film thickness and oxygen pressure. The electrical properties of transparent capacitors were investigated at various thickness of the dielectric layer. The capacitor shows an overall high performance, such as a high dielectric constant of 28 and a low leakage current of 2.03×10⁻⁶ A/cm² at ±5 V. Transmittance above 70% was observed in visible region.     

Structural,mechanical and electronic properties of sodium based fluoroperovskites NaXF3 (X=Mg,Zn) from first-principle calculations

The structural stability, mechanical, electronic and thermodynamic properties of the cubic sodium based fluoro-perovskite NaXF₃ (X=Mg, Zn) have been studied using density functional theory (DFT). The generalized gradient approximation of Perdew–Burke and Ernzerhof (GGA-PBE) is used for modeling exchange-correlation effects. In addition, the alternative form of the GGA proposed by Engel and Vosko (GGA-EV) is also used to improve the electronic band structure calculations. The results show that both compounds are stable in the cubic Pm3m structure. From Poisson׳s ratio, it is inferred that cubic anti-perovskite NaXF₃ are ductile in nature and that bonding is predominantly of ionic in nature. The electronic band structure calculations and bonding properties show that anti-perovskites have an indirect energy band gap (M–Г) with a dominated ionic character. The thermal effects on thermal expansion coefficient, Debye temperature and Grüneisen parameter were predicted using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. The calculations are found to be in good agreement with other results.     

Electronic structure,optical and dielectric constant of compounds Indium-based: InAlP2, and InGaP2 in its chalcopyrite,CuPt and CuAu-I structures

First principles calculations within the density functional theory framework were carried out to calculate electronic structures and dielectric constant predictions of InGaP₂ and InAlP₂ compounds. We use three arrangements of these compounds: CuAu-I, CuPt and chalcopyrite ones. Different approximations have been dealt with in order to predict valuable bands gaps energy using DFT calculations. Electronics structure results are promising, due to the good agreement with a number of observable physical-chemistry properties. On the other hand, electron localization function and atom in molecule formalisms have been done to give more insight on the bonding properties. Capabilities that exhibit the InAlP₂ in its CuAu-I structure, such as the anisotropy and second harmonic generation, make it promising for an intensive optoelectronic application.     

First-principles prediction of the structural and electronic properties of zinc blende GaNxAs1−x alloys

To investigate the structural and electronic properties of zinc blende GaN_xAs_1?x alloys, we performed full-potential linearized augmented plane wave (FP-LAPW) calculations based on density functional theory. We assessed GaN_xAs_1?x alloys for 0≤x≤1 using 16-atom special quasi-random structures. The generalized gradient approximation (GGA) of Wu and Cohen was used as the exchange correlation potential to calculate the structural and electronic properties of GaN_xAs_1?x. In addition, the alternative GGA proposed by Engel and Vosko and the modified Becke–Johnson potential were used for better reproduction of the band structure and electronic properties. The equilibrium lattice parameters and bulk modulus were calculated and analyzed for binary and ternary alloys. The lattice constants for GaN_xAs_1?x positively deviate from Vegard's law with an upward bowing parameter of ?0.4708 Å. All our materials are direct-bandgap semiconductors for which the valence band maximum is located at Γ_v and the conduction band minimum at Γ_c. We observed that the direct bandgap of GaN_xAs_1?x increases nonlinearly with x. To shed light on the bandgap trend for increasing nitrogen concentrations in GaN_xAs_1?x, we used the atoms-in-molecule formalism. Special attention was paid to the increase in charge transfer for the nitrogen atom and to ionicity as a function of increasing x concentration.     

An ab initio study of the structural,elastic, electronic,optical properties and phonons of the double perovskite oxides Sr2AlXO6 (X=Ta,Nb, V)

We report ab initio density functional theory calculations of the structural, elastic, electronic and optical properties of the double perovskite oxides Sr₂AlXO₆ (X=Ta, Nb, V). We have predicted a direct Г–Г band gap in Sr₂AlXO₆ (X=Ta, Nb) and an indirect Г–X band gap for Sr₂AlVO₆. The fundamental band gap increases linearly when the pressure is enhanced in the range 0–20 GPa. The frequency dependent of complex dielectric function, absorption, reflectivity and electron energy loss function were investigated in the range 0–40 eV. Features such as lattice constant, bulk modulus, elastic constants, band structure, total and local densities of states have been computed.     

Predicted Thermoelectric Properties of the Layered XBi<Subscript>4</Subscript>S<Subscript>7</Subscript> (X = Mn,Fe) Based Materials: First Principles Calculations

We report a theoretical investigation of electronic structures, optical and thermoelectric properties of two ternary-layered chalcogenides, MnBi₄S₇ and FeBi₄S₇ , by combining the first principles density functional calculations and semi-local Boltzmann transport theory. The calculated electronic band structure have demonstrated that both compounds exhibit indirect band gaps. The optical transitions are explored via the dielectric function (real and imaginary parts) along with other related optical constants including refractive index, reflectivity, and energy loss spectrum. These chalcogenides have exhibited interesting thermoelectric properties such as Seebeck’s coefficient, electrical and thermal conductivity, and power factor as function of temperatures.