Effect of Surface Functional Groups on the Electronic Behavior and Optical Spectra of Mn2N Based MXenes.

The extensive applications of MXenes, a novel type of layered materials known for their favorable characteristics, have sparked significant interest. This research focuses on investigating the influence of surface functionalization on the behavior of Mn2NTx (Tx=O2, F2) MXenes monolayers using the "Density functional theory (DFT) based full-potential linearized augmented-plane-wave (FP-LAPW)" method. We elucidate the differences in the physical properties of Mn2NTx through the influence of F and O surface functional groups. We found that O-termination results in half-metallic behavior, whereas the F-termination evolves metallic characteristics within these MXene systems. Similarly, surface termination has effectively influenced their optical absorption efficiency. For instance, Mn2NO2 and Mn2NF2 effectively absorb UV light ~50.15×104 cm-1 and 37.71×104 cm-1, respectively. Additionally, they demonstrated prominent refraction and reflection characteristics, which are comprehensively discussed in the present work. Our predictions offer valuable perspectives into the optical and electronic characteristics of Mn2NTx-based MXenes, presenting the promising potential for implementing them in diverse optoelectronic devices.

Proposal of new spinel oxides semiconductors ZnGaO2, [ZnGaO2]:Mn3+ and Rh3+: ab-initio calculations and prospects for thermophysical and optoelectronic applications.

Transparent conducting oxides (TCOs) of semiconductor family gained significant attention due to increasing trends in the optoelectronic and thermo-physical applications. In current work, we reported electronic, optical, transport and thermodynamical properties of spinel oxides ZnGaO2, [ZnGaO2]:Mn3+ and [ZnGaO2]:Rh3+ compounds. Based on DFT, we employed first-principles calculations implemented in Wien 2k using the modified-Becke-Johnson (mBJ) on parent spinel and generalized-gradient-approximation plus Hubbard potential U (GGA + U) on doped materials, respectively. The calculated band structure shows insulating nature of parent compound, while doped material observed semiconducting nature contains direct band gap for both spin channels with band gaps of [ZnGaO2]:Mn3+ (0.59 up, 2.4 eV dn) and [ZnGaO2]:Rh3+ (2.1 eV up/dn) respectively. The electronic and optical results reveal that hybridization occurred mainly due to O-p/Zn, Mn-d, Rh-d and Ga-s orbitals. It is analyzed that Mn-doped material shows good absorption in the visible region while other are good in UV region. The effective masses of spinel oxides are also computed at high symmetry directions hence varied nonlinearly with the doping. The stability of materials is checked by calculating formation energies which indicate Mn-doped spinel oxide is most stable as that of others. The thermoelectric properties of spinel oxides were carried out by Post-DFT (Boltztrap) calculations. Large values of Seebeck coefficient and power factor of Mn-doped spinel oxide indicate that this material can be used for thermoelectric devices. The thermodynamical properties are calculated by quasi-harmonic Debye model implemented in GIBBS 2 code. Moreover, the pressure and temperature dependence of all (TD) parameters of investigated spinel oxides are analyzed using quasi-harmonic Debye model.

Insights into the Impact of Yttrium Doping at the Ba and Ti Sites of BaTiO3 on the Electronic Structures and Optical Properties: A First-Principles Study.

We reported a systematic study of the effects of Y doping BaTiO3 at Ba and Ti sites. We assessed the structural, electronic, and optical properties by employing first-principles calculations within the Tran-Blaha-modified Becke-Johnson (TB-mBJ) potential and generalized gradient approximation + U approaches. We calculated the lattice constants and bond lengths for pure and Y-doped BaTiO3. We explored the consequences of electronic structure and optical property modification because of Y doping in BaTiO3. Indeed, Y doping has led to various modifications in the electronic structures of BaTiO3 by inducing a shift of the conduction band through lower energies for the Ba site and higher energies for the Ti site. It was found that Y doping, either at Ba or at Ti sites, strongly enhanced the BaTiO3 dielectric constant properties. The transformation in bonding was explored via the charge density contours and Born effective charges. We used the state of art of polarization theory based on finite difference and Berry-phase approaches to investigate piezoelectricity. Y doping has increased the dielectric constants but canceled the piezoelectricity as they changed to metallic nature. We could look into the future for potential doping, preserving the semiconductor nature of BaTiO3 and increasing the permittivity with large dielectric loss.

Density functional theory study of mixed halide influence on structures and optoelectronic attributes of CsPb(I/Br)3.

This paper reports on the influence of the bromine (Br) atoms substitution on the structures and optoelectronic traits of ${\text{CsPbI}_3}$CsPbI3, wherein the density functional theory (DFT) simulation was performed, using all electrons full potential linearized augmented plane-wave method. Furthermore, the generalized gradient approximation, local density approximation, and modified Becke-Johnson exchange-correlation potential were used to improve the optimization and band structure calculations. The calculated lattice constants of ${\text{CsPbI}_3}$CsPbI3 and ${\text{CsPbBr}_3}$CsPbBr3 were consistent with the experimental values. All the studied compounds revealed wide and direct bandgap energies at the R-symmetry point, which varied from 1.74-2.23 eV. The obtained refractive indices of the ${\text{CsPbI}_3}$CsPbI3, ${\text{CsPbBrI}_2}$CsPbBrI2, ${\text{CsPbIBr}_2}$CsPbIBr2, and ${\text{CsPbBr}_3}$CsPbBr3 compounds were correspondingly 2.265, 2.245, 2.090, and 2.086. Present findings may contribute towards the development of experimental studies on the proposed compounds with controlled properties useful for the solar cells.

Design and characterization of novel polymorphs of single-layered tin-sulfide for direction-dependent thermoelectric applications using first-principles approaches.

Advanced computational approaches have made the design and characterization of novel two-dimensional (2D) materials possible for applications in cutting-edge technologies. In this work, we designed five polymorphs of 2D tin sulfide (namely, α-SnS, ß-SnS, γ-SnS, δ-SnS, and ε-SnS) and explored their potential for thermoelectric applications using density functional theory-based computational approaches. Investigations of the energetic stability showed that the generated monolayers were as stable as parent α-SnS and exhibited cohesive and formation energies comparable to those of other stable 2D materials. These monolayers demonstrated high structural anisotropy (except ß-SnS), which resulted in interesting features in the effective mass of the charge carriers and the subsequent thermoelectric properties. The in-plane anisotropy yielded different effective masses of charge carriers along the 100- and 010-directions. The x- and y-components of the electrical conductivity tensors were accordingly enhanced by the p-type doping and n-type doping, respectively. We estimated the maximum thermoelectric power factors along the x- and y-axes and the corresponding optimal doping levels were recognized; this suggested that the thermoelectric performance of these monolayers along the x-direction can be improved by p-type doping and that along the y-direction can be improved by n-type doping. Moreover, the thermoelectric figures of merit of the SnS monolayers approached a benchmark value of unity at room temperature. Our results suggested that these novel polymorphs of 2D SnS are promising materials for applications in direction-dependent thermoelectric devices. The present study can provide valuable guidance for generating low-cost and non-toxic polymorphs of other layered-structure materials.

Optoelectronic properties of naphtho[2, 1-b:6, 5-b']difuran derivatives for photovoltaic application: a computational study.

Some important optoelectronic properties of naphtho[2,1-b:6,5-b']difuran (DPNDF) and its two derivatives have been limelighted by applying the density functional theory (DFT). Due to their low cost, high stability and earth abundance, the DPNDF and its derivatives are considered as potential organic semiconductor materials for their optoelectronics applications. Highly proficient derivatives are obtained systematically by attaching -CN (cyanide) to DPNDF at various sites. Our calculations indicate that DPNDF has a wide and direct band gap with an energy gap of 3.157 eV. Whereas the band gaps of its derivatives are found to be decreased by 88 meV for derivative "a" and 300 meV for derivative "b" as a consequence of p orbitals present in C and N atoms in derivative structures. The narrowing of the energy gap and density of states for the derivatives of DPNDF in the present investigation suggest that energy gap can be engineered for desirable optoelectronic applications via derivatives designing. Furthermore, their obtained results for optical parameters such as the dielectric and conductivity functions, reflectivity, refractive index, and the extinction coefficients endorses their aptness for optoelectronic applications. Graphical Abstract Real part of dielectric function for derivative "b".