Electron Energy Loss Function Research Articles

First-principles calculations of structural, magneto-electronic, mechanical, optical and thermoelectric properties of novel quaternary Heusler alloys type ZrCoYAs (Y= Fe and Mn)

To determine the structural, mechanical, electronic, magnetic, optical, and thermoelectric properties of novel quaternary Heusler alloys type ZrCoYAs (Y= Fe and Mn), we used DFT with WIEN2k. Our results showed that the ferromagnetic Y-type-III phase is more stable due to the higher negative values of their formation energy. We calculated and discussed the elastic constants Cij, which are used to calculate the mechanical properties. The Spin-polarized band structure and DOS calculations using the GGA-PBE and GGA + U approach display a metallic character. However, using the mBJ-GGA-PBE and mBJ-GGA + U approach show a half-metallic character, a semiconductor for the spin-down channel with a direct band gap of 0.61 eV with mBJ-GGA-PBE and 0.74 eV with mBJ-GGA + U for ZrCoMnAs and a direct band gap of 0.43 eV with mBJ-GGA-PBE and indirect band gap with 0.39 eV with mBJ-GGA + U for ZrCoFeAs, in contrast, the spin-up channel is metallic, with 100 % spin polarization and an integer magnetic moment of 1.00 μB for ZrCoMnAs and 2.00 μB for ZrCoFeAs, obeying the Slater-Pauling rule. The estimated Curie temperatures of ZrCoMnAs and ZrCoFeAs are 204 K using the new model, 421 K using MFA, and 385 K using the new model, 1627 K using MFA, respectively. As exchange-correlation potential, MBJ and MBJ + U provide a better description of the electronic and magnetic properties of ZrCoMnAs and ZrCoFeAs compounds. Important optical properties such as dielectric function, absorption coefficient, refractive index, optical conductivity, reflectivity, and electron energy loss function are calculated in the infrared, visible, and ultraviolet range. The static dielectric function suggests that ZrCoMnAs possesses greater polarizability. Both alloys exhibit similar behavior in the far ultraviolet region range and reach a maximum absorption in the ultraviolet range. The half-metallic character of both alloys is revealed from the reflectivity at zero frequency. The calculation of the thermoelectric properties shows positive Seebeck coefficients, indicating that these Heuslers are p-type. Furthermore, the highest power factor is observed at a temperature of 1400 K. The maximum value of ZT is ∼1.1 at 1400 K for ZrCoFeAs and ZrCoMnAs. These studies show that these alloys may have potential applications in the thermoelectric applications.

Electronic and optical characteristics of CaLiX3 (X = Cl, Br, I) perovskite compounds using the Tran–Blaha modified Becke–Johnson potential

We present the results of a comprehensive investigation using the full-potential linearized augmented plane wave approach to analyze the structural characteristics, electronic structures, and optical spectra of the perovskite compounds CaLiX3 (X = Cl, Br, or I). Various functionals were employed to simulate the exchange–correlation interactions. The calculated equilibrium structural parameters, obtained using the generalized gradient approximation, are consistent with the existing findings in the literature. The computed electronic structures reveal that the Tran–Blaha modified Becke–Johnson potential significantly enhances the bandgap. For all CaLiX3 compounds studied, we predicted an indirect bandgap. Additionally, we observed a gradual decrease in the bandgap as the atomic size of the X element increases. The electronic states constituting the various energy bands were evaluated by computing the partial and total densities of states. In addition, we computed a variety of optical spectra, including the complex dielectric function, absorption coefficient, refractive index, extinction coefficient, reflectivity, and electron energy loss function. The results demonstrate that a decrease in the bandgap leads to an increase in the zero-frequency limit of the dielectric function ε(0). The origins of the peaks and structures in the optical spectra were identified.

First-principles study on the structural, elastic, electronic, optical and thermophysical properties of NaNO3 and K-doped NaNO3

The current work illustrates the optical, thermophysical, electronic, elastic, and structural characteristics of pure and K-doped NaNO3 obtained using DFT calculations. Electronic characteristics such as band structure, projected and total density of states of pure and doped NaNO3 are analyzed where the calculated band gaps for pure and K-doped NaNO3 were discovered to be 3.05 eV and 2.90 eV, respectively. The Berry–phase calculations carried out on both systems showed the existence of ferroelectric polarization, where an enhanced spontaneous polarization value of 36 μC/cm2 for K-doped NaNO3, as compared to 20 μC/cm2 for intrinsic NaNO3 is obtained. The thermophysical properties such as bulk modulus (B0), Debye temperature (θ D), and specific heat capacity (Cv) were calculated over a wide temperature range from 0 K to 800 K. The linear optical properties namely the dielectric constant, refractive index, electron energy loss function, absorption and extinction coefficient are calculated in wide energy range from 0 to 30 eV and discussed in detail.

Tailoring the optoelectronic properties of MoS2 for broadband photodetection: Showcasing an Ab-into study involving the quasi-particle correction within the Green’s function-based approximation

In this study, the electronic and structural characteristics of both bulk and monolayer hexagonal MoS2 material are studied within and beyond density functional theory (DFT) by considering one-shot GW corrections for an accurate band gap prediction. Interestingly, our computed quasiparticle (QP) bandgap of 1.36 eV and 3.33 eV for bulk and monolayer, respectively, is in excellent agreement with the experimental finding. The elucidation of the optical properties was estimated with the aid of the Bethe–Salpeter equation within the many-body perturbation theory (MPB). The computed optical transitions such as absorption coefficient, extinction coefficient, refractive index, reflectivity, and electron energy loss function are in better agreement with the experimental data. Moreover, the new approach allows for the efficient inclusion of all conduction bands in GW calculations, significantly reducing computational costs compared to traditional methods. A good agreement of the lattice parameters, as well as the interlayer distance with the experimental findings, is observed by the inclusion of van der Waals (vdW) corrections. Besides the agreement with previously reported values, the evaluated band structure determined with the quasiparticle corrections shows that both bulk and monolayer MoS2 material exhibit semiconducting properties with direct and indirect band gaps, respectively. The calculation of the density of states reveals that the s-orbitals of S atoms and the d-orbitals of Mo are predominantly at the origin of the essential material properties secured at the Fermi level. The results of the study also point to the possibility of a foundation for creating physical structures with swift, decisive, directed, and long-range broadband photodetection capabilities.

External electric field assisted energy band gap modulation and optical properties of SiGe/AsSb heterobilayers

In this work, first-principle calculations within Density Functional Theory (DFT) were performed to study the structural, electronic, and optical properties of eight different bilayer van der Waals (vdW) heterostructures composed of SiGe and AsSb monolayers. These heterobilayers exhibit large energy bandgap (90 meV–459 meV) with linear energy–momentum relationship, implying high charge carrier mobility. Application of external vertical electric field can effectively modulate the energy bandgap of these heterobilayers from 64 meV to 459 meV, depending on stacking orders. Our study shows that a moderate amount of electric field can almost linearly tune the energy bandgap, however, semiconductor to metal transition occurs beyond a certain limit. The mechanism of energy bandgap tuning by the external electric field was examined by studying differential charge density. The optical properties such as complex dielectric function, electron energy loss function, complex refractive index, reflectivity, absorption coefficient, and optical conductivity of these SiGe/AsSb heterobilayers are studied for parallelly and perpendicularly polarized incident light. Our research demonstrates that these heterostructures exhibit variable plasma frequency depending on the stacking order of the heterostructures, anisotropic reflectivity i.e., birefringence properties in response to the incident light's polarization. Also, they exhibit high refractive indices (∼3) and absorption coefficients (∼105 cm−1) from visible to ultraviolet incident light frequencies. Our study proposes several SiGe/AsSb heterobilayers with unique electronic and optical properties which may have potential applications in nanoscale electronic and optoelectronic applications.

Topological semimetals in the ZrB5 (B = Se, Te) material class: Weyl points and electronic properties

In the present work, the electronic structure, elastic parameters, density of states (partial and total), optical properties, and charge density of ZrB5 (B = Se, Te) have been investigated by means of first principles calculations. The generalized gradient approximation has been used for modeling the exchange-correlation effects. It has been observed that the calculated lattice parameter values are in agreement with the values in the literature. The second-order elastic constants were calculated, and the other related quantities have also been estimated. The electronic band structures and the partial density of states corresponding to these band structures of ZrSe5 and ZrTe5 are examined, and it is understood that ZrTe5 and ZrSe5 are narrow band semiconductors or semimetals. Finally, the electron energy loss function (ELS) spectra and charge density of ZrB5 are calculated and interpreted.

CO adsorption on two-dimensional 2H-ZrO2 and its effect on the interfacial electronic properties: implications for sensing

Environmental pollution is commonly caused by direct and indirect greenhouse gasses and various traces of toxic gasses. CO is a tasteless, colourless and highly hazardous greenhouse gas that can bind with the hemoglobin much easier than oxygen. Materials with effective CO sensing capability are highly desirable. In this work, we have studied the repercussions of the molecular adsorption of toxic carbon monoxide (CO) on the structural, electronic, interfacial electronic and gas sensing properties of the two-dimensional (2D) 2H phase of zirconium dioxide (2H-ZrO2) using density functional theory (DFT) calculations. The most suitable adsorbent structure is screened out and interaction strengths between adsorbate molecule and adsorbent layer are provided in terms of binding energies. As a result of CO adsorption, the energy band gap (Eg) is altered and the resulting change in the conductivity of 2H-ZrO2 monolayer has implications for sensing. Energy band profiles relating to CO adsorbed 2H-ZrO2 reveal that fermi level shifts towards conduction bands exhibiting a development of n-type semiconducting character. Eg values relating to pristine and CO adsorbed 2H-ZrO2 sites such as TM, H, CB and B are 1.58, 1.98, 2.05, 2.06 and 2.03 eV, respectively. Further insights into the adsorption reveal that charge is accumulated near 2H-ZrO2 in the case of H and B adsorption sites, whereas for the case of TM and CB sites, depletion is noted. Essential gas sensing properties such as conductivity sensitivity (S), and recovery time (τ) are also reported. Notably, TM, CB, and B absorption sites depicted 17%, 2%, and 6% lower S values than H site. Furthermore, the H site achieved a shorter (32 ps) than the other adsorption sites. Response of pristine and CO adsorbed 2H-ZrO2 to that of incident photons is investigated with the help of real and imaginary parts [ and ] of complex dielectric function, electron energy loss function [] and joint density of states [] for a broader range of 0 to 10 eV. Major differences in dielectric function exist along in-plan and out-of-plan directions. After a detailed comparison, it is reported that more number of optical transitions exist between the linked states for the case of CO adsorbed 2H-ZrO2.

Achieving controllable multifunctionality through layer sliding

Dynamical variation of physical properties in a controllable fashion provides exciting possibilities to obtain multifunctional materials. In this work, layer-sliding is employed to modify the structural, interfacial electronic and optical properties of unintercalated and Mg-intercalated two-dimensional (2D) van der Waals heterostructure (vdW-HS) consisting of buckled silicene and hexagonal boron nitride (hBN). The most stable stacking configuration of silicene over hBN is screened out and then intercalated with Mg at the interface. Dynamical-dependent changes in the properties of vdW-HS are performed by sliding silicene over hBN monolayer in the absence and presence of the intercalant. Layer-sliding is carried out in equal length intervals, and various parametric quantities related to the physical characteristics of the vdW-HS are repeatedly calculated and compared. Apart from various parametric quantities, stability of unintercalated and Mg-intercalated vdW-HS is also checked by means of relative total energies, binding energies and vdW gaps along the sliding pathway. Comparison of binding energies shows that the un-slided, half-slided, and fully-slided Mg-intercalated vdW-HS are 1.52, 1.44 and 1.42 eV more stable than the unintercalated vdW-HS. Opening of a small band gap of 12, 31 and 28 meV for un-slided, half-slided and fully-slided unintercalated vdW-HS, respectively, is worth mentioning. To study the interfacial electronic behavior, planar average charge density difference (Δρ) and charge transfer (ΔQ) are also calculated and varied via layer-sliding. Further, we calculated diverse optical spectra such as the complex dielectric function (DF), electron energy loss function [L(ω)], diagonal components of dielectric tensor [ε(iω)], refractive index [n(ω)], extinction coefficient [k(ω)], absorption coefficient [α(ω)], and reflectivity [R(ω)] for un-slided, half-slided and fully-slided unintercalated and Mg-intercalated vdW-HS. Interestingly, the polarization and energy losses have been reduced in the case of Mg-intercalated vdW-HS. The suggested layer-sliding method can be established as a general scheme for bringing multifunctionality into a layered material.

Ab initio study of electronic structure, bonding and optical properties of ternary A2B2In (A = Ca, Eu and B = Pd, Pt) indides

Crystal structure, optical and electronic properties of metal rich intermetallic Ca2Pd2In, Ca2Pt2In, Eu2Pd2In and Eu2Pt2In compounds have been explored using density functional theory based orthogonalized linear combination of atomic orbitals (OLCAO) method and code. The local density approximation scheme has been employed to probe all the properties. The outcomes of the electronic structure revealed the conducting nature of ternary indides. Density of states plots of ternary indides exhibited an increased number of energy states moving from Ca2Pd2In, Ca2Pt2In, Eu2Pd2In to Eu2Pt2In at Fermi level which substantiate the metallic nature of these compounds. The localization index calculations reflected the highly delocalized states in the vicinity of Fermi level. The cationic behavior of Ca- and Eu-atoms and anionic character of Pd-, Pt-, In-atoms has been evaluated through the effective charge (Qα*) calculations. Bond order calculations indicated highest strength of Ca2Pt2In among the studied indides. Optical features in the form of complex dielectric function, optical conductivity and electron energy loss function have been thoroughly discoursed. Two eminent peaks in electron energy loss L(ω) spectra have been observed at 29.77 and 27.83 eV which are associated to the plasmonic resonance.

“Extraction and studies of optoelectrical parameters in LaFeO3-polyvinyl alcohol composite films for optoelectronic application”

Ceramic LaFeO3 (LFO) nanoparticles were synthesized using the solid state reaction method. To grow and study the various optoelectrical parameters of polyvinyl alcohol (PVA) and LFO-PVA nanocomposite films (wt%), the solution casting technique were used. To study optical properties, these films were subjected to Ultraviolet–Visible spectroscopy. From the UV–visible spectra, the high reflectance and low transmittance nature of the sample was observed. The refractive index and extinction coefficient of these films were obtained from reflectance and transmittance data. The optical results reveal that increasing LFO doping concentration decreases the energy band gap (Eg) values from 5.20 to 2.74 eV, while Urbach energy (Eu) increases from 0.423 eV to 4.871 eV. With doping, the value of single oscillator energy (Eo) decreases from 6.212 eV to 3.658 eV, while dispersion energy (Ed) increases from 8.481 eV to 158.92 eV. With LFO doping concentration, optical constants and parameters such as refractive index, extinction coefficient, dielectric constants and electron energy loss function were determined from transmittance and reflectance data. The refractive index (n) and extinction coefficient (k) are calculated to be in the ranges from 1.4 to 12 and 5.85 × 10−5 ‒ 26 × 10−3, respectively. The real (ε1) and imaginary (ε2) dielectric constants vary from 2 to 138.8 and 3.01 × 10−4 ‒ 3.25 × 10−2, respectively. The volume and surface energy loss functions were determined to be 1.96 × 10−4 ‒ 1.03 × 10−6 and 1.34 × 10−4 ‒ 3.14 × 10−7, respectively. The optical density and skin depth (δ) shows variation with filler concentration (wt%). The maximum optical conductivity σ1(ω) and σ2(ω) for 48% (wt%) sample were found to be 1.5 × 105 and 1.08 × 109 S−1 at 220 nm. The wavelength dependent real and imaginary parts of the optical dielectric functions and the WDD model were used to calculate the fundamental parameters, including Nopt/m*, ε∞, τ, μopt, ωp, ωd, ρopt, and n0. The value of Nopt/m* was increased from 8.61 × 1052 m3Kg−1 to 5.60 × 1054 m3Kg−1. The reflection loss (RL) and average molar refraction (Rm) were found to increase with doping concentration. For these samples, the optical non linear susceptibility (χ(3)) was determined to be in the range from 3.77 × 10−15 to 2.94 × 10−7. The value of electronic polarizability αp decreases from 2.57 × 10−23 to 7.33 × 10−24 for PVA, while for the composite films the value of αp increases from 7.81 × 10−25 to 3.59 × 10−24 in the wavelength range 200–1000 nm. Also, these calculated parameters shows a decreasing trend with LFO doping contents. It was further observed that the investigated parameters exhibit a strong dependence on the LFO doping content. Based on these optoelectronic properties of this material, it could be used for possible optoelectronic applications.

Structural, electronic, optical, mechanical and magnetic properties of Co2CrZ (Z = As, B, Ga, Pb) full-Heusler compounds

Two separate computational algorithms have been used in the current investigation of Full-heusler compounds. One is the pseudo-potential approach used in the Atomistic Tool Kit-Virtual Nanolab, while the other is FP-LAPW method as implemented in WIEN2k. In the computational code, these compounds exhibit mattelic character in both the majority and minority spin channels. According to the WIEN2k and ATK-VNL codes, the computed magnetic moments of these compounds Co2CrZ (Z = As, B, Ga, and Pb) are 4.93 µB and 5.02 µB, 3.00 µB and 3.08 µB, 3.02 µB and 3.16 µB, and 4.07 µB and 4.30 µB, respectively. Between the estimated value and the Slater-Pauling rule, we discovered excellent agreement. These compounds' optical characteristics include reflectivity, refractive index, excitation coefficient, and absorption coefficient, among others. An analysis has been done on the electron energy loss and optical conductivity. Both the electron energy-loss function and the absorption coefficient increase as the energy value increases. As per the results of elastic properties, Co2CrZ compounds with Z = As, Pb are ductile by nature, whereas those with Z = B, Ga are brittle. Co2CrZ (Z = As, B, Ga, and Pb) compounds exhibit metallic behaviour when their Cauchy pressure (CP = C12 - C44) value is positive.

Ab-initio study about the electronic structure, optical, and transport properties of novel AIn2O4 (A = Ca, Sr, and Na) materials

Here, using first-principles calculations within the framework of density functional theory, we reported results relating to the structural stability, electronic, optical, and thermoelectric properties of AIn2O4 (A = Ca, Sr, and Na) spinel oxides. Among the three materials CaIn2O4, and NaIn2O4 have a direct bandgap semiconductor nature, whereas the SrIn2O4 shows an indirect bandgap semiconductor nature. These materials’ broad energy bandgaps reveal that the bonds present are strongly covalent in nature. The results of the band structures are also strongly supported by the calculated density of states for the three materials, which also validates their semiconducting nature. Our calculated density of states plots shows an overall similarity trend, indicating that the top of the valence bands in the CaIn2O4 materials originate primarily from the p-states and for SrIn2O4, and NaIn2O4 are due to the s-states of the oxygen anions. Additionally, the linear optical constants like the complex dielectric function, the refractive index, the electron energy loss function, the absorption coefficient, and the reflectivity spectra of these novel spinel oxides are computed and examined in detail for their possible applications in optoelectronic devices. The thermoelectric transport parameters were also calculated, and the findings obtained are presented in depth, indicating that these materials are suitable for thermoelectric device applications. Essentially, the present effort must assist the progress of discrete and integrated semiconductor device applications.

Charge Carrier Statistics-Based Analytical Model and Simulation of Optical Mechanisms in White Graphene for High-Quality FETs and Optoelectronic Applications

The aim of the present paper is to investigate the scaling behaviors of charge carriers and optical mechanisms in white graphene. The approach in this work is to provide analytical models for carrier velocity, carrier mobility, relaxation time and optical mechanisms of white graphene such as optical conductivity, absorption, transmittance, reflectivity, extinction coefficients and electron energy loss function. For doing so, one starts with identifying the analytical modeling of carrier concentration in the degenerate and nondegenerate regions. The computational models of carrier velocity, mobility and relaxation time with numerical solutions are analytically derived, in which the normalized Fermi energy, carrier concentration and temperature characteristics dependence are highlighted. Moreover, the optical mechanisms of white graphene are analytically modeled based on degenerate conductance. The proposed analytical models demonstrate a rational agreement with our simulation results and previous experiments in terms of trend and value. The remarkable properties of white graphene mentioned in this paper and obtained results bring new hopes for using of white graphene as a good substrate for nanomaterials such as graphene, germanene, stanene and silicene in electronics and optoelectronic applications.

The physical properties of RbAuX (X = S, Se, Te) novel chalcogenides for advanced optoelectronic applications: An ab-initio study

The efficient physical properties of alkali-based ternary chalcogenides are investigated in the orthorhombic structure employing the full potential linearized-augmented-plane-wave (FP-LAPW) method within the context of the density functional theory. The used modified Becke-Johnson (mBJ) potential confirms an indirect bandgap nature in the RbAuS and a direct bandgap in the RbAuSe and RbAuTe materials. The computed bulk modulus confirms that RbAuS material is more stable and resistive as compared to RbAuSe and RbAuTe materials. Additionally, linear optical parameters such as the dielectric function, the electron energy loss function, the absorption coefficient, the reflectivity, and the refractive indices have been calculated and discussed extensively. A greater static dielectric constant value is observed for a smaller bandgap value, which verifies Penn’s model. The optical absorption plots indicate that these materials absorb more in the visible region. Some strong sharp peaks in the reflectivity spectra in the ultraviolet region were noticed suggesting them to be promising shielding-type materials against the UV rays. Furthermore, the thermoelectric transport properties are calculated, and the presented results in detail, suggesting that the studied materials are efficient for applications involving thermoelectric devices.

First-principles assessments of the electronic, and magneto-optical characteristics of Fe–Mn co-doped anatase TiO2 for photo-catalysis applications

First principles modeling is conducted to scrutinize the structural, chemical, electronic structures, bonding character, and magneto-optical features of intrinsic or pure anatase TiO2, Fe or Mn single-atom doped, and Mn–Fe diatom co-doped anatase TiO2 systems, respectively. Herein, the spin-polarized density functional theory (DFT) concerted with the on-site Hubbard (U) correction scheme for the Coulomb interaction, is utilized for the exchange-correlation term, as the generalized gradient approximation (GGA)+U. The spin-polarized density of states of Mn mono-atom doped anatase TiO2 material indicated a magnetic semiconductor attribute for both down/up spin components. Conversely, the outcome spin-polarized density of states of both Fe-doped and Mn–Fe co-doped anatase TiO2 materials illustrated the emergence of an intermediate band behavior. Accordingly, three magnetic impurity bands are produced in Mn–Fe co-doped anatase TiO2, the first two spin-up bands are located just uppermost the valence states nearby the Fermi level and the third spin-up/down band is lying far from the Fermi level just below the minimum conduction band. Interestingly, the spin-polarized charge density displayed an orbital ordering between the O 2p-orbitals and 3d-orbitals of Mn–Fe doped diatoms in the host TiO2 anatase system. The valuable optical ingredients, such as the optical absorption coefficient, refractive index, reflectivity spectra, optical conductivity, and electron energy loss function, are inspected and discussed. Moreover, the optical absorption coefficient characteristics of the mono-doped Mn/Fe and Mn–Fe co-doped TiO2 anatase structure displayed a relocation in the absorption feature edges towards the visible electromagnetic radiation regime. This means that the induced impurity bands delineate the essential contributor for boosting the catalytic activity in the visible light. It is expected that the Fe–Mn co-doped anatase TiO2 system could be a compelling candidate for its ultimate use in the photo-catalysts or magnetic storage devices.

Pressure effects on the opto-electronic and mechanical properties of the double perovskite Cs2AgInCl6

The double perovskite Cs2AgInCl6 is a potential material for the absorbing layer of a thin film solar cell due to its direct band gap. The only current limitation the material has is its wide band gap. A careful engineering of its structural, mechanical and opto-electronic properties with the aid of hydrostatic pressure ranging from 0 GPa16 GPa has been studied using density functional theory. The calculations were carried out using GGA-PBEsol (Perdew–Burke–Ernzerhof revised for solids) exchange correlation functional. It is found that the lattice constant reduces as the pressure increases, while the bulk modulus increases as the exerted pressure increases. The bulk moduli calculated from the elastic constants are found to be in agreement with those obtained via Birch-Murnaghan equation of state. This indicates the accuracy of the calculations, and it is achieved at all pressure values. The mechanical properties of the material are investigated, and the material is found to be anisotropic and ductile at all pressure considered. Due to the underestimation of the energy band gap by GGA-PBEsol exchange correlation functional, Tran-Blaha modified Burke Johnson (TB-mBJ), a metaGGA functional, was used to calculate the electronic and optical properties. The energy band gap is found to reduce from 2.746 eV at ambient pressure to 2.482 eV at 6 GPa and momentarily increases until it reached 2.501 eV at 16 GPa. The optical properties of Cs2AgInCl6 revealed its absorption threshold is in the visible range, although a shift in the absorption threshold is observed as pressure is applied on it. An 8.7 % increase in the refractive index is observed as pressure increases. The calculated absorption coefficient corresponds reasonably with the calculated band gap. The electron energy loss function and reflectivity of the material have also been investigated.

Study of the Structural, Electronic and Optical Properties of 1T-ZrX<sub>2</sub> Materials (X=S, Se, Te)

The Electronic and optical properties of zirconium dichalcogenides (ZrS2,ZrSe2, andZrTe2),have been explored via ab-initio methods based on the density functionaltheory (DFT) within the frame of generalized gradient approximation (GGA) and a couplingtechnique between the plane wave (PW) and the pseudo-potential (PP) approaches. Theobtained results showed that ZrS2 and ZrSe2 are semiconducting materials with energy gapsof 1.15 eV and 0.3 eV respectively from the valence band maximum located at G point andthe conduction band minimum located at L point, while ZrTe2 showed a metallic characterwith a density of states at the Fermi level of about 0.8 states/eV. Based on a Kramers–Kroniganalysis of the reflectivity, we have obtained the spectral dependence of the real andimaginary parts of the complex dielectric function (ε1 and ε2, respectively) and the refractiveindex (n). The collected data were used for the calculation of absorption coefficient,reflectivity index, conductivity, and electron energy loss function of ZrS2, ZrSe2, and ZrTe2 forradiation up to 20 eV. All three chalcogenides were found to be good absorbers of ultravioletradiation. The reflectivity of ZrS2 is low in the visible and near-ultraviolet region butincreases sharply for higher photon energies and approaches 96% at ~18.5 eV. The R(ω) spectrum of ZrTe2, on the other hand, is non-selective and remains above 50% over a widerange of energies from infrared to ultraviolet which suggeststhe potential application of thismaterial as an effective solar reflector. On the other hand, the refractive indices of ZrS2, ZrSe2,and ZrTe2 in the visible range are high. The optical spectra show moderate anisotropy concerning the electric field polarization of the incident light.

Stibnite at modified Becke-Johnson exchange potential

The demand for cheaper, nontoxic and earth-abundant materials as absorbing layer for solar cell is immensely needed to replace scarce, toxic and expensive one. In this regard, chalcogenide materials have considerably attracted the attention of a lot of researchers because of showing a great potential for different applications. Stibnite (Sb2S3), a chalcogenide binary material is intensively investigated for exploiting its potential for different energy technologies being a less toxic, abundantly available, stable and efficient one, which are the fundamentals for sustainability as well as to realize the dream of green energy. In this study, a computational study of the structural, electronic and optical properties of the stibnite (Sb2S3) crystal structure is presented using the full potential (FP) linearized augmented plane wave (LAPW) method framed within the density functional theory (DFT). For the estimation of the exchange-correlation potential part, besides the local density approximation (LDA), Wu-Cohen parameterized generalized gradient approximation (WC-GGA) Perdew-Burke-Ernzerhof parameterized generalized gradient approximation (PBE-GGA), and Perdew-Burke-Ernzerhof generalized gradient approximation for solids and surfaces (PBEsol-GGA), the Trans-Blaha approach of the modified Becke-Johnson (TB-mBJ) potential is used to improve the fundamental band gap value. Moreover, these calculations are performed by involving spin-orbit coupling (SOC) contribution as well. Additionally, optical properties, such as imaginary and real parts of the dielectric function, optical conductivity absorption coefficient, refractive index, reflectivity, and electron energy loss function were investigated as well. The obtained results of the band gap energy and optical properties with TB-mBJ potential were found closer to the experimental data and endorse its potentiality for the photovoltaics applications.

Theoretical investigation of some fundamental physical properties of the ternary nitrides Ca4SiN4 and Ca4GeN4 under pressure and temperature effect

We reported for the first time a theoretical study of structural, electronic, optical, elastic and thermodynamic properties of Ca4SiN4 and Ca4GeN4, based on DFT + PP-PW approach. The calculated structural parameters are in good agreement with the experimental data. Both considered alkaline earth metalloid nitrides are more compressible along the c-axis. The band structure calculations showed that the studied compounds are direct bandgap (Γ¬Γ) semiconductors; the energy bandgap given by GGA (LDA) is equal to 1.501 (1.598) eV and 1.462 (1.583) eV for Ca4SiN4 and Ca4GeN4, respectively. The optical parameters including dielectric function, refractive index, extinction coefficient, absorption coefficient, reflectivity and electron energy-loss function were computed for different polarizations of the incident light. Single-crystal elastic constants, polycrystal elastic moduli and their pressure dependence were calculated and discussed. The two nitrides satisfy the mechanical stability criteria over the considered pressure range. We have also investigated their thermodynamic properties by computing Debye temperature, thermal expansion coefficient α and heat capacities CP and CV.

Exploring the electronic and optical anisotropy of quasi-one-dimensional ternary chalcogenide CrSbSe3: a DFT study

The anisotropy of the electronic and optical properties of the quasi-one-dimensional ternary transition metal chalcogenide CrSbSe3 is investigated using density functional theory (DFT) including the on-site Coulomb self-interaction potential (DFT + U) and spin-orbit interaction. The compound is an indirect bandgap semiconductor with bandgap of 0.58 eV. Effective masses and charge recombination rates along different directions show appreciable anisotropy, indicating the possibility of sensor applications. CrSbSe3 exhibits satisfactorily high carrier mobility and charge recombination rates along all directions, making it suitable for solar and photovoltaic applications. The Se-p and Cr-d orbitals contribute to the DOS in the valence band, while DOS contribution to the conduction band bottom comes mainly from Sb-p and Cr-d orbitals. Simulated XPS and HAXPES show that for soft x-rays, the peak in the low binding energy is due to the electron emission from Se-p and Cr-d orbitals while the peak in the high binding energy is due to the electron emission from Cr-d and Se-s orbitals. For hard x-rays, the relative intensity of the low binding energy peak decreases in comparison to the high binding energy peak, indicating enhanced electron emission from Se-s orbitals at higher energy x-rays. CrSbSe3 possesses large anisotropy in optical parameters such as refractive index, optical absorption, reflectivity, optical conductivity and optical extinction. The birefringence and dichroism are large in the IR, visible and near UV regions, with a giant birefringence equal to 0.56 at 650 nm and dichroism equal to 0.57 at 550 nm. The electron energy loss function is anisotropic for high energetic electrons, while for electrons below 4 eV it is isotropic. CrSbSe3 is an ideal material for photovoltaic, sensor and other optoelectronic applications as it possesses a bandgap of 0.58 eV, large optical anisotropy, high values of dielectric constant, refractive index, absorption coefficient and extinction coefficient.