D. P. Rai

GGA + U and mBJ + U study of the optoelectronic, magnetic and thermoelectric properties of the SmAlO3 compound with spin–orbit coupling

The electronic, thermoelectric, optical, and magnetic properties of the samarium aluminate (SmAlO3) compound is studied using the spin-polarized full-potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT). The exchange and correlation potential is treated with the generalized gradient approximation (GGA) and the Coulomb repulsion (U = 0.51 Ry) has been calculated theoretically and was used for the GGA + U based approximated electronic structures. Additionally, the modified Becke–Johnson (mBJ) potential was also utilized along with the GGA + U approach for the calculation of the band gap. On the other hand, the optical properties were analyzed with the mBJ + U results and the thermoelectric properties were explained on the basis of the electronic structures and density of states (DOS) with a thermoelectric efficiency of 0.66 at 300 K. The minimum reflectivity at 1.13 eV (which was equal to 1.097 μm) was found to be in agreement with the experimental results. Further refinements in the electronic structures were obtained by adding the spin–orbit coupling (SOC) interactions to the GGA + U approach, which was then combined with the mBJ approximations. Hence, a conclusion using the combined mBJ + U+SOC study indicates that the SmAlO3 compound is a potential candidate for both thermoelectric as well as magnetic devices.

Electronic structure and x-ray spectroscopy of Cu2MnAl1–xGax

We explore the electronic and related properties of Cu2MnAl1–xGax with a first-principles, relativistic multiscattering Green function approach. We discuss our results in relation to existing experimental data and show that the electron-core hole interaction is essential for the description of the optical spectra especially in describing the X-ray absorption and magnetic circular dichroism spectra at the L2,3 edges of Cu and Mn.

Effects of hydrogen and nitrogen impurities on electronic, structural and optical properties of 2D ZnS graphene based

Ab initio calculations based on density functional theory (DFT) were used to investigate the structural, electronic and optical properties of ZnS graphene based (GB) with N and H atoms as ligands. These studies were conducted using the generalized gradient approximation (GGA) by means of WIEN2k package and revealed how the electronic and optical properties of GB structures of ZnS, including density of electron states, the energy band structure, the dielectric function, the energy loss function, the refractive index, the reflection and absorption rates, are modified by the effects of H and N impurities. Band structure analysis indicated that ZnS GB is a semiconductor with direct band gap (3.4xa0eV) in Γ direction. Furthermore, it has been found that H (ligand) and N (ligand) atoms that bond to a Zn atom cause magnetic and half-metallic behaviors, and one or two electronic states appeared in the energy gap at down spin for H and N ligands, respectively.

Studying structural, electronic and optical properties of zinc-blende Ga1−x Al x P at normal and under pressure by means of first principle

Structural, electronic and optical properties of the zinc-blende Ga1−x Al x P ternary alloys with their ordered AlP and GaP binary compounds have been investigated, using the full potential linearized augmented plane wave method in conjunction with the density functional theory. The total energies are carried out to calculate the lattice constant, bulk modulus and its pressure derivative of the zinc-blende AlP, GaP binary compounds and their corresponding ternary Ga1−x Al x P solid solutions for the compositions (x = 0.25, 0.50 and 0.75). The band gap energies and the optical properties of these materials are investigated at normal pressure condition as well as under high pressure levels. The estimated results obtained from this work are justified, discussed and compared with the experimental data and other available theoretical works.

Effect of Si and Ge Surface Doping on the Be 2 C Monolayer: Case Study on Electrical and Optical Properties

The electronic and optical properties of X (Si, Ge) doped Be2C monolayer has been investigated using the all-electron full potential linear augmented plane wave (FP-LAPW + lo) method in a scalar relativistic version as embodied in the Wien2k code based on the density functional theory. Using cohesive energy calculation, it has been shown that the Si and Ge doped to Be2C monolayer have stable structures and the doping processes modified the direct band gaps. The calculated electronic band structure confirm the direct band gap nature since the conduction band minimum and the valence band maximum are located at the center of the Brillouin zone. The total and partial density of states help to gain further information regarding the hybridizations and the orbitals which control the energy band gap. The calculated optical properties help to gain deep insight into the electronic structure. Our calculated results indicate that the X (Si, Ge) doped Be2C monolayer can be have potential application in optoelectronics devices.

Theoretical analysis of the electronic, optical and thermal properties of lead strontium telluride alloys Pb1−xSrxTe (x = 0.0−1.0)

Abstract We have simulated different physical properties of Pb1−xSrxTe semiconductors, using the Ab-initio full potential augmented plane wave (FP-LAPW) method. The two commonly used exchange potentials viz., PBE-GGA and WC-GGA are used along with the most recently developed modified Becke and Johnson (mBJ) potential to study the electronic and optical properties. In this study, we have observed an increase in band gap values as well as the lattice parameter with increasing the concentration of Sr atoms in Pb1−xSrxTe alloys while the bulk modulus and the refractive index have reverse effect. The microscopic origin of the band gap bowing is explained using the approach of Zunger and co-workers. At ambient conditions (p = 0, T = 0), the calculations indicate that Pb1−xSrxTe is a direct band gap semiconductor R–R with x = 0.125, 0.25, 0.375, 0.5, 0.625, 0.75 and 0.875. The refractive indices are also calculated using the FP-LAPW method and the models of Moss, Ravindra and the Herve–Vandame. The obtained results are in consistent with the previous available data. To study the thermal effects, the temperature effect on the lattice parameters, thermal expansions, heat capacities the quasi-harmonic Debye model is applied. The Debye temperature is determined from the non-equilibrium Gibbs function.

Electronic and Magnetic Properties of Fe Atomic Chain and Fe Atomic Plane: An ab initio Study

The electronic and magnetic properties of Fe atomic wire and atomic plane have been theoretically investigated from full potential linearized augmented plane wave (FPLAPW) method within a frame work of density functional theory (DFT). This work is based on the comparative study of number of Fe nanochains with infinite length and infinitely spread Fe nanosheet. A most commonly adopted GGA approximation is used for electron exchange correlation. In our calculation, the property of Fe-chain is predicted to be magnetic metal with the presence of deep valley (in Spin-up DOS) and a peak (in Spin-down DOS) at Fermi level (EF) shows the antisymmetric DOS. The presence of antisymmetric DOS is a signature of exchange splitting between the degenerated d-states. The splitting between t2g states is very prominent in Fe-chain which enhances the magnetic moment. The magnetic moment decreases with the increase in number of Fe-chains.

Investigation of doped Perovskite systems RAIO3 using density functional theory based electronic structure and thermoelectric studies

Samarium doping effects on the thermoelectric properties in Eu1-xSmxAlO3 (x=0%, 50%, and 100%) were studied using first principles calculations based thermal transport property measurement. The result indicate that the compound is an intrinsic n-type material. Samarium doping has a positive effect on the overall thermoelectric performance of the Eu1-xSmxAlO3 system, with sharp increase in figure of merit (ZT) observed when x=0, 50 and 100% up to 150K. Compared to x=0 and 100%, the case of x=50% was found to have more positive increment in ZT value suggesting that the doing to have positive effect on figure of merit in Eu1-xSmxAlO3. Furthermore, all the samples show stable thermoelectric compatibility factors over a broad temperature range from 700 to 1000 K, which could have great benefits for their practical applications. It is concluded that the overall thermoelectric performance of the Eu1-xSmxAlO3 could be highly enhanced using doping techniques.

Study of 4f electron based compound Sm1-xGdxAlO3, a thermoelectric (TE) material: FP-LAPW method

Gadolinium doping effects on the thermoelectric properties in Sm1-xGdxAlO3 (x=0%, 50%, and 100%) were studied using first-principles calculations based thermal transport property measurement. The result indicates that the compound is an intrinsic n-type material. Samarium doping has a positive effect on the overall thermoelectric performance of the Sm1- xGdxAlO3 system, with a sharp increase in the figure of merit (ZT) observed when x=0, 25, 50, 75 and 100% up to 800K. Compared to x=0 and 100%, the case of x=50% was found to have a more positive increment in ZT value suggesting that the doping to have a positive effect on the figure of merit in Sm1-xGdxAlO3. Furthermore, all the samples show stable thermoelectric compatibility factors over a broad temperature range from 700 to 1000 K, which could have great benefits for their practical applications. It is concluded that the overall thermoelectric performance of the Sm1-xGdxAlO3 could be highly enhanced using doping techniques.