Search

Hydrogen is considered an alternative source of energy to fossil fuels for the fulfilment of current energy demands. Photocatalysis initiates the hydrogen evolution reaction which is believed to be the greenest approach to produce hydrogen through clean, safe, and environmentally friendly methods. In this Review, we focus mainly on the comprehensive analysis of the 2D and 3D bulk materials on the basis of their superior photocatalytic activities. However, several literatures have reported the superiority of 2D material over the bulk counterpart in terms of photocatalytic performance owing to their ultrathin layered structures, offer a higher surface-to-volume ratio, flexibility, large active sites for incoming H2O molecules, etc. We have thoroughly analysed the drawbacks of various hydrogen production methods focusing on the photocatalysis mechanism and the processes of evolution of hydrogen. In addition to this, a short overview of the various solid-state materials for photocatalysis that have been developed so far and their mechanisms are discussed. Lastly, we have discussed the recent developments in 2D materials and their composites as promising photocatalysts.

Pb-based perovskites are considered to be the most efficient materials for energy harvest. However, real-time application is limited because of their toxicity. As a result, lead-free perovskites that offer similar advantages are potential alternatives. Here, we have chosen LiSnX$_3$ (X = Cl, Br, and I) for further calculation and explore its possibilities for harvesting clean and green energy. Our objective is to examine strategies for optimizing the parameters that control the energy-harvesting capabilities, particularly the interplay between structural variations and electrical properties. The density functional theory (DFT) has been employed for the theoretical simulation. Within the DFT framework, we have studied the effect of applied pressure (0 to 20 GPa) and elemental substitution on their physical properties. We hereby report the variation of lattice parameters, elastic constants, band gaps, and piezoelectric constants. MD simulation with time steps of up to 5 ps was performed to verify structural stability at room temperature. We report the semi-conducting characteristic of LiSnX$_3$ and the high piezoelectric response up to 20.7 Cm2. The presence of high piezoelectric coefficients suggests that manipulation of the structure of LiSnX$_3$ may provide an alternative way to harvest energy through electromechanical processes.

Wide bandgap semiconductors (WBGs) are predicted to be the potential materials for energy generation and storing. In this work, we used density functional theory (DFT) that incorporates generalized gradient approximation (GGA) and meta-generalized gradient approximation (mGGA) methods to explore the various properties of the LiSnCl3 and LiSnBr3 perovskites. The structural stabilities, charge transfer, electronic, optical, mechanical, and piezoelectric properties are studied. Herein, we report that these rarely studied materials are eco-friendly and look promising for optoelectronics and piezoelectric applications.

Recently, a new magnetic phase, termed altermagnetism, has caught the attention of the magnetism and spintronics community. This newly discovered magnetic phenomenon differs from traditional ferromagnetism and antiferromagnetic. It generally lacks net magnetization and is characterized by unusual non-relativistic spin-splitting and broken time-reversal symmetry. This leads to novel transport properties such as the anomalous Hall effect, the crystal Nernst effect, and spin-dependent phenomena that cannot be fully explained by traditional magnetic theories. Spin-dependent phenomena such as spin currents, spin-splitter torques, and high-frequency dynamics emerge as key characteristics in altermagnets. This paper reviews the main aspects pertaining to altermagnets by providing an overview of theoretical investigations and experimental realizations. We discuss the most recent developments in altermagnetism, its comparison to other magnetic orders, and future prospects for exploiting its unique properties in next-generation devices.

This work presents a detailed study of the electronic structure, phonon dispersion, Z2 invariant calculation, and Fermi surface of the newly discovered kagome superconductor CsV3Sb5, using density functional theory (DFT). The phonon dispersion in the pristine state reveals two negative modes at the M and L points of the Brillouin zone, indicating lattice instability. CsV3Sb5 transitions into a structurally stable 2x2x1 charge density wave (CDW) phase, confirmed by positive phonon modes. The electronic band structure shows several Dirac points near the Fermi level, with a narrow gap opening due to spin-orbit coupling (SOC), though the effect of SOC on other bands is minimal. In the pristine phase, this material exhibits a quasi-2D cylindrical Fermi surface, which undergoes reconstruction in the CDW phase. We calculated quantum oscillation frequencies using Onsager's relation, finding good agreement with experimental results in the CDW phase. To explore the topological properties of CsV3Sb5, we computed the Z2 invariant in both pristine and CDW phases, resulting in a value of (u0; u1u2u3) = (1; 000), suggesting the strong topological nature of this material. Our detailed analysis of phonon dispersion, electronic bands, Fermi surface mapping, and Z2 invariant provides insights into the topological properties, CDW order, and unconventional superconductivity in AV3Sb5 (A = K, Rb, and Cs)., Comment: To be published in APL Quantum

In this paper, we have analysed the electronic and mechanical properties of Nitrogen(N) doped (6,1) SWCNTs based on first-principles and Molecular dynamic (MD) simulation. A schematic N-doping on SWCNT was performed along zigzag(zz) and armchair(ac) direction. Armchair doping is considered parallel to the tube axis while the zigzag is along the cross-section perpendicular to the tube axis. In doping pattern (both zz and ac) we have observed the variation in electronic properties for even number of N-doping and odd number of N-doping. To study the mechanical properties we have adopted ab-initio MD-simulations. We report the dependence of the tensile response of the tube on the dopant concentration and doping pattern. The single N-doped system shows enhanced tensile stress by 55% as compared to the pristine SWCNT. While the variation of young's modulus for all N-doped systems are almost invariant.

First Principles calculations are performed on the cubic bulk and its (001) surface of CsPbBr3 to reveal its electronic and optoelectronic properties. Various calculation schemes like GGA, GGA+SOC and the highly accurate modified Becke Johnson potential (mBJ) are applied. The electronic energy band gap calculations obtained from mBJ shows close approximity with the available experimental results. The cubic bulk phase is investigated for its mechanical stability and is found to bypass other structural phases. The optical absorption of both the bulk and the surface surpasses non-lead based cubic halides and zinc-based organic-inorganic hybrids.

The recent progress in the field of hydrogen storage in carbon and boron nitride nanostructures has been summarized. Carbon and boron nitride nanostructures are considered advantageous in this prospect due to their lightweight and high surface area. Demerits of pristine structures to hold hydrogen molecules for mobile applications have been highlighted by many researchers. In such cases, weak van der Waals interaction comes into account, hence, the hydrogen molecules are weakly bonded with the host materials and hence weak adsorption energy and low hydrogen molecules uptake. So, to tune the adsorption energy as well as overall kinetics, methods such as doping, light alkali-alkaline earth metals decoration, vacancy, functionalization, pressure variation, application of external electric field, and biaxial strain has been adopted by many researchers. Physisorption with atoms decoration is promising for hydrogen storage application. Under this condition, the host materials have high storage capacity with considerable average adsorption energy, feasible adsorption/desorption kinetics.

Lightweight 2D materials due to its large surface area are being studied for its hydrogen storage applications. The characteristics of hydrogen adsorption on the electric field-induced h-BN bilayer were investigated. The overall storage capacity of the bilayer is 6.7 wt% from our theoretical calculation with E ads of 0.308 eV/H$_2$. The desorption temperature for H$_2$ molecules from the h-BN bilayer system in the absence of an external electric field is 243 K. With the introduction of an external electric field, the E$_{\rm ads}$ lies in the range 0.311-0.918 eV/H$_2$ with a desorption temperature of 245-725 K. The charge transfer analysis reveals that 0.001-0.008 |e| of electronic charge transfer between the h-BN bilayer and H$_2$ molecules. Henceforth, the adsorption mechanism is through a weak Van der waals interaction. Our results show that the external electric field enhances the average adsorption energy as well as the desorption temperature and thus making the h-BN bilayer a promising candidate for hydrogen storage.

We report the structural, mechanical, electronic, optical, thermoelectric properties and spectroscopic limited maximum efficiency (SLME) of oxide double perovskite structure Ba2SbNbO6 and Ba2SbTaO6 compounds. All the investigations were performed through the first-principles density functional theory (DFT). The obtained values for the elastic constants reveal the mechanical stability of the studied compounds. The calculated data of bulk modulus (B), shear modulus (G), and Young's modulus (E) for Ba2SbTaO6 are found to be greater than those of Ba2SbNbO6. The ratio of Bulk to shear ratio (B/G) shows that Ba2SbNbO6 and Ba2SbTaO6 are ductile. The computed electronic band structure reveals the semiconducting nature of both compounds. We have also studied the electron relaxation time-dependent thermoelectric properties, such as Seebeck coefficient, thermal conductivity, electrical conductivity, thermoelectric power factor, and the figure of merit as a function of chemical potential at various temperatures for p-type and n-type charge carriers. The high absorption spectra and good figure of merit (ZT) reveal that both the studied compounds, Ba2SbXO6 (X = Nb, Ta) are promising materials for photovoltaic and thermoelectric applications. The calculated SLME of 26.8% reveals that Ba2SNbO6 is an appealing candidate for single-junction solar cells.

A comparative study of wurtzite ZnO doped by rare earth elements (Tm, Yb, Ce) have been investigated using density functional theory (DFT) based on the full-potential linearized augmented plane wave orbital (FP-LAPW) method, as implemented in Wien2K code. The structural parameters were calculated by PBEsol functional and in good agreement with the experimental data. The electronic (density of states, band structure) and optical (absorption coefficient, reflectivity, refraction index) properties were determined by TB-mBJ potential. The rare earth element doped ZnO have a significant impact on the optoelectronic properties which are mainly arise due to the presence of 4f electrons. The results of electronic structure shows that the doping of Tm, Yb, Ce on pristine ZnO has increases the band gap and in qualitative agreement with the experimental results. In many cases the Fermi level has been shifted to the conduction band, revealing n-type characters. Electrical conductivity has been calculated using BoltzTrap code based on the semiclassical equation of Boltzmann. It has been observed that the conductivity has a direct relation with the temperature and carriers concentration. Our results provide the basis for future research in Tm, Yb, Ce doped ZnO compounds used as integrated optoelectronic devices and solar cells.

We investigated the electronic and optical properties of bilayer AB stacked Boron and Nitrogen vacancies in hexagonal Boron Nitride (h-BN) using density functional theory (DFT). The density of states (DOS) and electronic band structure showed that Boron vacancy in bilayer h-BN results in a magnetic and conducting ground state. The band gap energy ranges from 4.56 eV for the pristine BN bilayer to 0.12 eV for a single Nitrogen vacancy in the bilayer. Considering the presence of 1,3,4-Boron vacancy, half metallic character is observed. However, the 2-boron vacancy configuration resulted in metallic character. The bilayers with 1,2,3,4- Nitrogen vacancy has a band gap of 0.39, 0.33, 0.28 and 0.12eV respectively, which is significantly less than the pristine band gap. Also B and N vacancy induces ferromagnetism in the h-BN bilayer. The maximum total magnetic moment for the Boron vacant system is 6.583uB in case of 4-Boron vacancy configuration. In case of Nitrogen vacancy system it is 3.926uB for 4-Nitrogen vacancy configuration. The optical response of the system is presented in terms of the absorption coefficient, refractive index and dielectric constant for pristine as well as the defective configurations. Negative value of dielectric constant for Boron vacant system in the energy range 0.9-1.4 eV and for Nitrogen vacant system in the energy range 0.5-0.8 eV opens an opportunity for it to be utilized for negative index optical materials. The current study shows that B and N vacancies in bilayer h-BN could have potential applications in nano-structure based electronics, optoelectronics and spintronic devices.

Half-metallicity, low magnetic damping and high curie temperature (TC) are crucial for application in spintronics and full Heusler alloys in this regard exhibit remarkable properties. Herein, we have considered Co2FeAl (CFA) and Fe2CoAl (FCA) as a representative of direct and indirect full Heusler compounds which crystallises in L21 and C1b phases, respectively. The theory of L21 type Heusler alloys has been well established, however the fundamental understanding of Fe2CoAl is still under developed. In this paper, we have employed density functional theory (DFT) to study the electronic, elastic and X-ray spectroscopic properties of Co2FeAl and Fe2CoAl. The electron exchange correlation were treated within a generalized gradient approximation (GGA) as PBE-scheme. In order to include the impact of valence electrons an onsite Coulomb potential is added to GGA as GGA+U. Within both GGA and GGA+U, CFA shows a half-metallic behaviour but FCA is metallic. The calculated values of magnetic moment and TC are in close agreement with the experimental data.

We explore the electronic and related properties of Cu$_{2}$MnAl$_{1-x}$Ga$_{x}$ 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 L$_{2,3}$ edges of Cu and Mn., Comment: 6 pages, 4 figures

We explore the structural, electronic, mechanical and thermoelectric properties of a new half Heusler compound, HfPtPb which is all metallic heavy element and has been recently been proposed to be stable [Nature Chem 7 (2015) 308]. In the present work, we employ density functional theory and semiclassical Boltzmann transport equations with constant relaxation time approximation. The mechanical properties such as Shear modulus, Young modulus, elastic constants, Poisson ratio, and shear anisotropy factor are investigated. The elastic and phonon properties reveal that this compound is mechanically and dynamically stable. Pugh and Frantsevich ratio demonstrates the ductile behavior and Shear anisotropic factor reflects the anisotropic nature of HfPtPb. The calculation of band structure predicts that this compound is semiconductor in nature with band gap 0.86 eV. The thermoelectric transport parameters such as Seebeck coefficient, electrical conductivity, and electronic thermal conductivity and lattice thermal conductivity have been calculated as a function of temperature. The highest value of Seebeck coefficient is obtained for n-type doping at optimal carrier concentration. We predict the maximum value of the figure of merit 0.25 at 1000 K. Our investigation suggests that this material is n-type semiconductor., Comment: 14 pages, 5 Figures, 2 Tables

First-principles density functional theory (DFT) is used to investigate the electronic and magnetic properties of Sr$_4$Rh$_3$O$_{10}$, a member of the Ruddlesden-Popper series. Based on the DFT calculations taking into account the co-operative effect of Coulomb interaction ($U$) and spin-orbit couplings (SOC), Sr$_4$Rh$_3$O$_{10}$ is found to be a half metallic ferromagnet (HMF) with total angular moment $\mu_{\rm {tot}}$=12$\mu_B$ per unit cell. The material has almost 100$\%$ spin-polarization at the Fermi level despite of sizable SOC. Replacement of Rh atom by the isovalent Co atom is considered. Upon full-replacement of Co, a low-spin to intermediate spin transition happens resulting in a HMF state with the total angular moment three-time larger (i.e. $\mu_{\rm {tot}}$=36$\mu_B$ per unit cell), compared to Sr$_4$Rh$_3$O$_{10}$. We propose Sr$_4$Rh$_3$O$_{10}$ and Sr$_4$Co$_3$O$_{10}$ as candidates of half metals., Comment: 11 pages, 5 figures, Materials Science (cond-mat.mtrl-sci), Spintronics