Narrow Results

DFT is used for making first-principles calculations of electronic and optical properties of V₂O₅ in its orthorhombic phase, by employing Augmented Plane Waves$+$local orbital method with Generalized Gradient Approximation and Perdew–Burke–Ernzerhof potential to account for exchange–correlation interactions. The stability of the material is checked through the calculation of cohesive energy and Bader charge analysis is done to find out the electronic charges on different atoms in the unit cell. A DOS gap of about 2.1eV and a direct band gap of about 1.85eV just above the Fermi level is found to occur on using DFT, which is lower than the experimental value of 2.77eV. On using the DFT$+$U method, with $U=4.0$eV for Vanadium, a DOS gap of about 2.8eV and an indirect band gap of about 3.0eV are found to occur, which are closer to the experimental result, showing that the DFT+U method better accounts for electronic properties of V₂O₅. The optical properties, such as dielectric function, reflectivity, absorption coefficient, optical conductivity, refractive index, extinction coefficient and electron energy loss function also investigated for V₂O₅ by using DFT.

In this work, we delve into the investigation of the structural, electronic, and optical properties of Ba₂NbBiS₆ and Ba₂TaSbS₆ chalcogenide-based double perovskites, which are structured in the cubic space group $Fm\bar{3}m$ form. We have performed first-principles calculations using density functional theory (DFT) to study the above properties. The electronic band structure and density of states of this compound have been investigated, and their results show that Ba₂NbBiS₆ and Ba₂TaSbS₆ exhibit a semiconducting nature with an indirect energy gap of 1.680eV and 1.529eV, respectively. Furthermore, an investigation was conducted on the optical properties of the compounds throughout the energy range spanning from 0eV to 55eV. This investigation focused on many parameters, including dielectric functions, optical reflectivity, refractive index, extinction coefficient, optical conductivity, and electron energy loss. The optical data obtained from the calculations reveals that all compounds demonstrate isotropy in optical polarization. Furthermore, it has been noted that our compounds exhibit absorption properties inside the ultraviolet (UV) region. Consequently, these materials hold promise as potential candidates for various applications, such as UV photodetectors, UV light emitters, and power electronics. This is primarily attributed to their inherent absorption limits and the presence of prominent absorption peaks in this spectral range. In brief, chemical mutation techniques have been employed to manipulate the characteristics of double-sulfide perovskites to develop durable and environmentally friendly perovskite materials suitable for solar purposes.

This study provides a thorough analysis of magnesium oxynitride (MgON), employing first-principles calculations to investigate its potential for electronic, thermoelectric, and optical applications. The main objective was to comprehend the fundamental electronic, thermoelectric, and optical parameters of MgON using density functional theory (DFT) calculations. In electronic properties, the density of states (DOS) spectra revealed the significant contribution of Mg-s and O-p states for pristine MgO, while N-p states provide the maximum contributions with overlapping at the Fermi level in nitrogen-containing compositions. The band structure depicted a direct nature for undoped and doped MgO, and the bandgap of compositions was observed to decrease with the increment in nitrogen concentration. The thermoelectric properties of pure and N-doped MgO compositions were evaluated, which showed significant variations with an increase in temperature and doping. Furthermore, the optical properties of MgON were inspected and found to enhance optical conductivity, and absorption coefficient, whereas the refractive index and dielectric constant decrease at specific energy regions for elevated dopant content, which suggests its suitability for optoelectronic applications. Overall, this study reveals the versatility of MgON, making it a potential candidate for advanced electronic, thermoelectric, and optical applications.

This paper presents a simulation of the structural and optoelectronic properties of Scandium Arsenide (ScAs) and Aluminum Arsenide (AlAs) compounds. Theoretical modeling was performed using ab initio first-principles calculations, specifically the density functional theory (DFT), and the Mindlab numerical software. The software used two methods: the full-potential muffin-tin orbital method (FP-LMTO) and the full-potential plane-wave method (FP-LAPW). These two methods are employed to solve the Schrödinger equation. The exchange correlation effects have been computed using two different approximations: the generalized gradient approximation (GGA) and the local density approximation (LDA). Our findings indicate that the zinc blende structure (B3) is the stable phase, while the Wurtzite phase (B4) is metastable for the AlAs compound. On the other hand, the ScAs compound crystallizes in the NaCl phase (B1). The AlAs compounds undergo three phase transitions: $\mathrm{\text{B3}}\to \mathrm{\text{B4}}$, $\mathrm{\text{B3}}\to \mathrm{\text{B2}}$ and $\mathrm{\text{B3}}\to \mathrm{\text{B1}}$. In contrast, ScAs does not undergo any transition. The obtained results for equilibrium energies, lattice parameters and gap energies are in closer agreement with the experimental and theoretical data. The AlAs compound exhibits a semiconducting character, while ScAs exhibits a semi-metallic character. Additionally, the refractive index of these two compounds is similar to that of silicon, which is crucial for their application in photovoltaic cells.

In this paper, we present the implementation of the Density Functional Theory (DFT) method using the Geant4-DNA framework in the Single Instruction Single Data (SISD) mode. Furthermore, this implementation is improved in terms of execution time within the GeantV project with vectorization techniques such as Single Instruction Multiple Data (SIMD). Within this framework, a set of SIMD strategies in molecular calculation algorithms such as one-electron operators, two-electron operator, quadrature grids, and functionals, was implemented using the VecCore library. The applications developed in this work implement two DFT functionals, the Local Density Approximation (LDA) and the General Gradient Approximation (GGA), to approximate the molecular ground-state energies of small molecules and amino acids. To assess the performance of the implementations, a standard test simulation was performed in multiple CPU platforms. The SIMD vectorization strategy significantly accelerates DFT calculations, leading to time ratios ranging from 1.6 to 5.4 in either individual steps or entire implementations when compared with the scalar process within Geant4.

The influence of incorporating iron on the electronic structure, magnetic and optical properties of zigzag (10,0) boron nitride nanotubes (BNNTs) was investigated using first-principles calculations. The structures were incorporated with Fe according to B1$-x$Fe xN at various (x) contents (0.10, 0.20 and 0.30). Our calculations exhibited that adding additional Fe atoms reduced the energy gap of the structure. Incorporating more iron atoms creates additional sharp peaks within Fermi levels that come from the contribution of Fe-3d states. Doping with (Fe) also introduced magnetic moments in the BNNT structure. The optical parameters of the Fe-incorporated boron nitride nanotube are calculated. The real part of the dielectric function of pristine BNNT started to increase up to the middle of the UV region and then rapidly decreased between the wavelength range of 310–390 nm. Also, the pure boron nitride nanotube has no absorption in the visible light range and only detects UV radiation. The optical calculations showed that incorporating Fe shifted the absorption peaks of BNNTs into risky UV radiations, which helps researchers develop a vision for controlling and developing advanced materials for various electronic applications.

Investigation electron transport via molecular nanoscale junctions is one of the fundamental steps in developing improved high-performance thermoelectric materials for cooling and converting waste heat into electricity. Density functional theory (DFT) and non-equivalent Green’s function are applied to investigate the electric and thermoelectric properties of Fullerene $({\text{C}}_{60})$ doped with three metalloid ions from the periodic table. The M@C${}_{60}$ (M = P, As and Se) systems have two types of electrodes (gold and graphene). The results show that the electric conductance of G with gold leads is higher than the conductance attached to the graphene leads. Also, ${\text{C}}_{60}$ doped by Se is the best compared with P and as for both gold and graphene electrodes. Moreover, the calculations of HOMO-LUMO resonance shifted toward the high energy (low wavelength) in order $\mathrm{\text{Se}}>\mathrm{\text{P}}>\mathrm{\text{As}}$ due to the electronegativity, which is ordering $\mathrm{\text{Se}}>\mathrm{\text{P}}>\mathrm{\text{As}}$, with the Fano-resonance fixed around E–E${}_F=0$. Meanwhile, the value of Seebeck coefficient S for graphene leads is higher than S linked to the gold lead. Also, the merit figure for ZT and thermal electricity has been investigated.

The electronic band structure of AlN, AlSb, AlAs and their ternary alloys with In has been investigated by ETB. The ETB method has been formulated for sp³d² basis and nearest neighbor interactions of the compounds and its energy parameters have been derived from the results of the present first principles calculations carried on AlN, AlSb and AlAs. It has been found that the present ETB energy parameters can produce the band structure of the compounds and their ternary alloys with In successfully.

The electronic band structure of GaN and GaAs has been investigated by ETB to obtain the band gap bowing of In_xGa_1-xAs_1-yN_y alloys lattice matched to GaAs. The ETB method has been formulated for sp³d² basis and nearest neighbor interactions of the compounds, and its energy parameters have been derived from the results of the present first principles calculations carried out on GaN and GaAs. It has been found that the present ETB energy parameters are capable of producing the electronic band structure of corresponding compounds and the large bowing parameter of InGaAsN alloy.

We investigated the electron transport properties of thiophen-bithiol-based molecular wires through atomic metal–thiophen–metal systems using the first principle methods. Various metal–thiophen–metal atomic systems are constructed with different end atoms (S, Se, and Te). The electron transport of the atomic system is systematically studied by analysis of transmission function, density of states, and current–voltage characteristics of the systems.

First principles total energy calculations within the density functional formalism have been used to investigate the electronic, mechanical, and optical properties of pseudocubic-Si₃P₄ and Ge₃P₄. Considering the technological importance of the Si/Ge-Group-V elements, we have concentrated mainly on the comparatively less studied, but energetically more favorable pseudocubic-Si₃P₄ and Ge₃P₄ structures of the Si and Ge phosphides. We find that the electronic band structures show that pseudocubic-Si₃P₄ and Ge₃P₄ are both indirect band semiconductors with very low density functional band gaps of 0.24 eV and 0.13 eV, respectively. We also calculate mechanical properties of the materials, such as the bulk modulus, elastic constants, shear modulus, and Vickers hardness of the two phosphides. We find that the bulk and shear modulus of pseudocubic-Si₃P₄ and Ge₃ P₄ are 76.18 GPa and 58.37 GPa, and 59.99 GPa and 46.92 GPa, respectively. Pseudocubic-Si₃P₄ and Ge₃ P₄ have low Vickers hardness, nearly 18.88 and 16.86 GPa, respectively. Moreover, optical parameters, including dielectric function, refractive index, optical absorption, energy loss function, and plasma frequency are also studied.

A survey of recent studies of biaxial liquid crystals (LCs), whose nematic and/or smectic-A phases do not possess optical uniaxiality (viz., more than one optical axis exists), is given in this review. In particular, we emphasize on how Nuclear Magnetic Resonance (NMR) spectroscopy can help to advance the understanding of phase biaxiality in general, and to examine recent debates on the existence of biaxial nematic phase reported in low molecular mass bent-core or V-shaped mesogens. A general discussion of orientational order parameters is detailed, particularly in smectic-C (SmC) and biaxial nematic phases. How these orientational order parameters can be determined by various techniques such as NMR, IR absorbance and Raman scattering studies, will be mentioned. Recent X-ray observations of SmC clusters in the nematic phase of V-shaped mesogens are highlighted and contrasted with probable theory. Moreover, deuterium and carbon-13 NMR techniques are briefly reviewed, and their possible utilization to identify phase biaxiality in these biaxial LC systems is explored.

We adapt the classical Ornstein-Zernike equation for the direct correlation function of classical theory of liquids in order to obtain a model for the exchange-correlation hole based on the electronic direct correlation function. Because we explicitly account for the identical-particle nature of electrons, our result recovers the normalization of the exchange-correlation hole. In addition, the modified direct correlation function is shorted-ranged compared to the classical formula. Functionals based on hole models require six-dimensional integration of a singular integrand to evaluate the exchange-correlation energy, and we present several strategies for efficiently evaluating the exchange-correlation integral in a numerically stable way.

The study of bimetallic catalysts has scientific and technologic importance because of special catalytic activity towards several reactions. RhCu is an interesting bimetallic system due to combination of the very different catalytic activities of Rh and Cu. The catalytic activity of this bimetallic does not result from simple interpolation of the constituents. In fact, at low Cu content, the catalytic activity of RhCu is superior to that of Rh but when the Cu content is higher the activity decays. This is a curious trend which theoretical works had attempted to explain. This paper reports an overview of the most recent research works about this bimetallic system with emphasis in its especial characteristics.

The quest for novel low-dimensional materials has led to the discovery of graphene and thereafter, a tremendous attention has been paved in designing of its fascinating properties aiming in fabricating electronic devices. Using first-principles calculations, we study the structure, energetic and electronic as well as magnetic properties of graphene induced by the interactions in presence of both external and internal foreign agents in detail. We find that a variety of tunable electronic states, e.g., semiconductor-to-half-metal-to-metal and magnetic behaviors can be achieved under such hierarchical interactions and their influence. We also find that the nature and compositions of foreign substances play a key role in governing the electro-magnetic characteristics of these nanomaterials. In this review, we suggest a few routes for engineering the tunable graphene properties suitable for future electronic device applications.

Electronic band structure and optical parameters of ZnAl₂O₄ are investigated by first-principles technique based on a new potential approximation, known as modified Becke–Johnson (mBJ). This method describes the excited states of insulators and semiconductors more accurately The recent direct band gap result by EV-GGA is underestimated by about 15% compared to our band gap value using mBJ-GGA. The value of the band gap of ZnAl₂O₄ decreases as follows: E_g(mBJ-GGA/LDA) > E_g(GGA) > E_g(LDA). The band structure base optical parametric quantities (dielectric constant, index of refraction, reflectivity and optical conductivity) are also calculated, and their variations with energy range are discussed. The first critical point (optical absorption's edge) in ZnAl₂O₄ occurs at about 5.26 eV in case of mBJ. This study about the optoelectronic properties indicates that ZnAl₂O₄ can be used in optical devices.

Density functional theory (DFT) is performed to study the structural, electronic and optical properties of cubic fluoroperovskite AMF₃ (A = Cs; M = Ca and Sr) compounds. The calculations are based on the total-energy calculations within the full-potential linearized augmented plane wave (FP-LAPW) method. The exchange-correlation potential is treated by local density approximation (LDA) and generalized gradient approximation (GGA). The structural properties, including lattice constants, bulk modulus and their pressure derivatives are in very good agreement with the available experimental and theoretical data. The calculations of the electronic band structure, density of states and charge density reveal that compounds are both ionic insulators. The optical properties (namely: the real and the imaginary parts of the dielectric function ε(ω), the refractive index n(ω) and the extinction coefficient k(ω)) were calculated for radiation up to 40.0 eV.

In the present study, ground state and elastic properties of semiconductor MgSe in zinc-blende phase are investigated using density functional theory (DFT). Exchange-correlation potentials are approximated with the generalized gradient approximation (GGA). From the calculated bulk modulus, we determine the refractive index, plasmon energy, cohesive energy and micro-hardness of the MgSe semiconductor binary alloy. The density of state (DOS), projected density of state (PDOS), phonon dispersion frequencies, charged density, electronic band structure and dielectric functions are also reported. From the band structure, a direct band gap of 2.50 eV was observed in close agreement with other reported calculations, but lower than the experimental value of 3.60 eV. Along the high symmetries directions, we found a striking resemblance between MgSe and a III–V semiconductor, while the high cohesive energy in MgSe suggests filled bonding orbitals which might result in decrease in atomic volume with corresponding increased compression of the s-orbitals under any transition series.

Bonding nature as well as structural, optoelectronic and thermal properties of the cubic XMg₂O₄(X = Si, Ge) spinel compounds have been calculated using a full-potential augmented plane-wave plus local orbitals (FP-APW+lo) method within the density functional theory. The exchange-correlation potential was treated with the PBE-GGA approximation to calculate the total energy. Moreover, the modified Becke–Johnson potential (TB-mBJ) was also applied to improve the electronic band structure calculations. The computed ground-state parameters (a, B, B′ and u) are in excellent agreements with the available theoretical data. Calculations of the electronic band structure and bonding properties show that these compounds have a direct energy band gap (Γ-Γ) with a dominated ionic character and the TB-mBJ approximation yields larger fundamental band gaps compared to those obtained using the PBE-GGA. Optical properties such as the complex dielectric function ε(ω), reflectivity R(ω) and energy loss function L(ω), for incident photon energy up to 40 eV, have been predicted. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the effects of pressure P and temperature T on the thermal expansion coefficient, Debye temperature and heat capacity for the considered compounds are investigated for the first time.

We present the results of a density functional theory study of high-pressure structures of HgTe up to bcc structure, which is the highest-pressure structure that has been fully characterized in experiments in the compounds. We investigated the different structures of HgTe and studied the semimetal → semiconductor → conductor transition in detail. We found, in the mechanism for the semimetal → semiconductor transition, the local structure plays a very important role. Change in local structure leads to the change in hybridization of bonding, sp³ →sp³d² and led to the change from semiconductor to conductor. In addition, we focused on the special transition of semimetal → semiconductor. The tiny change of bond angle reduces the p–d repulsion interaction in the compound and a band gap is open up, which indicates the semiconductor property.