Bandgap engineering to tune the optical properties of Be_xMg_(1-x)X(X=S, Se, Te) alloys

Structural, electronic, and optical properties of alloys BexMgl-xX （X = S, Se, Te） in the assortment 0 〈 x 〈 1 were theoretically reported for the first time in zinc-blende （ZB） phase. The calculations were carried out by using full-potential linearized augmented plane wave plus local orbitals （FP-LAPW＋lo） formalism contained by the framework of density functional theory （DFT）. Wu--Cohen （WC） generalized gradient approximation （GGA）, based on optimization energy, has been applied to calculate these theoretical results. In addition, we used Becke and Johnson （mBJ-GGA） potential, modified form of GGA functional, to calculate electronic structural properties up to a high precision degree. The alloys were composed with the concentrations x = 0.25, 0.5, and 0.75 in pursuance of ＇special quasi-random structures＇ （SQS） approach of Zunger for the restoration of disorder around the observed site of alloys in the first few shells. The structural parameters have been predicted by minimizing the total energy in correspondence of unit cell volume. Our alloys established direct band gap at different concentrations that make their importance in optically active materials. Furthermore, density of states was discussed in terms of the contribution of Be and Mg s and chalcogen （S, Se, and Te） s and p states and observed charge density helped us to investigate the bonding nature. By taking into consideration of immense importance in optoelectronics of these materials, the complex dielectric function was calculated for incident photon energy in the range 0--15 eV.

Theoretical investigation of optical properties and band gap engineering for Zn1-xTMxTe(TM=Fe,Co)alloys by modified Becke-Johnson potential

The direct band gap ZnTe with transition metal （TM） impurities plays a vital role in optoelectronic and spintronic applications. In the present study, we use the advanced modified Becke-Johnson （mBJ） functional for performing the structural computations and detailed investigations of the optical characters in Zn1_xTMxTe （TM = Fe, Co） alloys with 0 ≤ x ≤1. By employing the FP-LAPW method, we determine various optical parameters for the ternary alloys and for the end binaries. The calculated static dielectric constants and optical band gaps for Zn1_xTMxTe （TM = Fe, Co） have an inverse relation that verifies the Penn model. We find that the static dielectric constant is nearly equal to the square of the static refractive index, and both increase with TM content. Furthermore, we also find a slight shift of peaks to a higher energy region with increasing TM concentration. The decreasing band gap and high value of the absorption in the visible region of electromagnetic spectrum make these alloys suitable for photonic and solar cell applications.

Electronic and thermoelectric properties of alkali metal-based perovskites CsYbF3 and RbYbF3

The electronic and thermoelectric properties of alkali metal-based fluorides CsYbF3 and RbYbF3 are studied by using Wien2k and BoltzTraP codes.The structural and thermodynamic stability of these materials are confirmed by tolerance factor(0.94 and 0.99 for RbYbF3 and CsYbF3)and negative formation energy.The optimized lattice constants and bulk moduli are consistent with the results reported in the literature.The reported band gap for RbYbF3 is 0.86 eV which decreases to 0.83 eV by the replacement of Cs with Rb.The electrical and thermal conductivities along with Seebeck coefficients decrease with temperature rising from 0 K to 800 K.The large values of thermoelectric parameters for positive chemical potentials show that the character is dominated by electrons.The studied materials have figures of merit 0.82 and 0.81 at room temperature respectively,for RbYbF3 and CsYbF3 and increase with temperature rising.Therefore,the materials under study may have potential application values in thermoelectric generators and refrigerators.

Magnetism,optical,and thermoelectric response of CdFe_2O_4by using DFT scheme

Comparative analysis of electronic, magnetic, optical, and thermoelectric properties of CdFe2O4, calculated by em- ploying PBEsol ＋ mBJ has been done. The PBEsol reveals metallic nature, while TB-mBJ illustrates ferromagnetic semiconducting behavior. The reasons behind the origin of ferromagnetism are explored by observing the exchange, crystal field, and John-Teller energies. The optical nature is investigated by analyzing dielectric constants, refraction, absorption coefficient, reflectivity, and optical conductivity. Finally, thermoelectric properties are elaborated by describing the electri- cal and thermal conductivities, Seebeck coefficient, and power factor. The strong absorption for the visible energy and high power factor suggest CdFe2O4 as the potential candidate for renewable energy applications.

Ab-initio investigation of AGeO_3(A=Ca, Sr) compounds via Tran Blaha-modified Becke Johnson exchange potential

We employ ab-initio calculations to analyze the mechanical, electronic, optical and also thermoelectric properties associated with AGeO3（A = Ca, Sr） compounds. The full-potential linearized augmented plane wave（FP-LAPW） technique in the generalized gradient approximation（GGA-PBEsol） and the lately designed Tran-Blaha-modified Becke-Johnson exchange potential are utilized to examine the mechanical and optoelectronic properties respectively. To explore the thermoelectric quality, we use the semi-classical Boltzmann transport theory. The particular structural stabilities regarding AGeO3（A = Ca, Sr） materials are validated simply by computations from the elastic constants. The energy band structural framework and the density of states are displayed to indicate indirect bandgap under ambient conditions. The particular computed optical attributes that reveal prospective optoelectronic applications are usually elucidated simply by studying ε1（0） and also Eg, which can be connected by means of Penn＇s design. The optical details uncover the actual suitability to power ranging products. Finally, the Boltz Tra P code is executed to analyze the actual thermoelectric properties, which usually presents that the increase of internal temperatures can enhance the electric conductivity, thermal conductivity and also the power factor, whilst Seebeck coefficient decreases. Therefore, the studied materials will also be ideal for thermoelectric products to understand helpful option for alternative energy resources.

Ab-initio calculations of bandgap tuning of In1-xGaxY(Y=N,P)alloys for optoelectronic applications

The III–V alloys and doping to tune the bandgap for solar cells and other optoelectronic devices has remained a hot topic of research for the last few decades.In the present article,the bandgap tuning and its influence on optical properties of In1-xGaxN/P,where(x=0.0,0.25,0.50,0.75,and 1.0)alloys are comprehensively analyzed by density functional theory based on full-potential linearized augmented plane wave method(FP-LAPW)and modified Becke and Johnson potentials(TB-mBJ).The direct bandgaps turn from 0.7 eV to 3.44 eV,and 1.41 eV to 2.32 eV for In1-xGaxN/P alloys,which increases their potentials for optoelectronic devices.The optical properties are discussed such as dielectric constants,refraction,absorption,optical conductivity,and reflection.The light is polarized in the low energy region with minimum reflection.The absorption and optical conduction are maxima in the visible region,and they are shifted into the ultraviolet region by Ga doping.Moreover,static dielectric constant e1(0)is in line with the bandgap from Penn’s model.