Pressure effect on structures and optoelectronic attributes of mixed halide CsPb(I/Br)3: a density functional theory study.

The effect of pressure (up to 10 GPa) on the electronic and optical properties of bromine-substituted cesium lead iodide (CsPbI3), as one promising inorganic halide perovskite, is investigated using modified Backe-Johnson (mBJ) potential for the first time to our knowledge. The lattice parameters, electronic bandgap, and imaginary and real parts of the dielectric function, along with the optical absorption coefficient, are calculated. Density functional perturbation theory is employed to compute the optical properties in the photon energy range from 0.0 to 30 eV. No structural or phase-type transformation is noticed under the applied pressure, which resulted in a uniform contraction of the unit cell. Bandgap variation is seen in all the structures, with the maximum (1.65 eV) and minimum (1.46 eV) decrease found for doped and undoped CsPbBrI2, respectively. The present work provides useful information about the performance of CsPbI3-xBrx compounds under high pressure that can be utilized in designing solar cells and optoelectronics.

Achieving controllable multifunctionality through layer sliding.

Dynamical variation of physical properties in a controllable fashion provides exciting possibilities to obtain multifunctional materials. In this work, layer-sliding is employed to modify the structural, interfacial electronic and optical properties of unintercalated and Mg-intercalated two-dimensional (2D) van der Waals heterostructure (vdW-HS) consisting of buckled silicene and hexagonal boron nitride (hBN). The most stable stacking configuration of silicene over hBN is screened out and then intercalated with Mg at the interface. Dynamical-dependent changes in the properties of vdW-HS are performed by sliding silicene over hBN monolayer in the absence and presence of the intercalant. Layer-sliding is carried out in equal length intervals, and various parametric quantities related to the physical characteristics of the vdW-HS are repeatedly calculated and compared. Apart from various parametric quantities, stability of unintercalated and Mg-intercalated vdW-HS is also checked by means of relative total energies, binding energies and vdW gaps along the sliding pathway. Comparison of binding energies shows that the un-slided, half-slided, and fully-slided Mg-intercalated vdW-HS are 1.52, 1.44 and 1.42 eV more stable than the unintercalated vdW-HS. Opening of a small band gap of 12, 31 and 28 meV for un-slided, half-slided and fully-slided unintercalated vdW-HS, respectively, is worth mentioning. To study the interfacial electronic behavior, planar average charge density difference (Δρ) and charge transfer (ΔQ) are also calculated and varied via layer-sliding. Further, we calculated diverse optical spectra such as the complex dielectric function (DF), electron energy loss function [L(ω)], diagonal components of dielectric tensor [ε(iω)], refractive index [n(ω)], extinction coefficient [k(ω)], absorption coefficient [α(ω)], and reflectivity [R(ω)] for un-slided, half-slided and fully-slided unintercalated and Mg-intercalated vdW-HS. Interestingly, the polarization and energy losses have been reduced in the case of Mg-intercalated vdW-HS. The suggested layer-sliding method can be established as a general scheme for bringing multifunctionality into a layered material.

Controlled dynamic variation of interfacial electronic and optical properties of lithium intercalated ZrO2/MoS2 vdW heterostructure.

Efficient strategies for modifying the characteristics of van der Waals (vdW) layered materials in a precise and reversible mode remain challenging. Our suggested method for customization entails the implementation of layer-sliding and intercalation. In this work, a norm-conserving approach within the context of density functional theory has been used to examine the electronic and optical properties of two-dimensional (2D) van der Waals heterostructure (vdWHS), which is modeled by using 2D zirconium dioxide (1T-ZrO2) and molybdenum disulfide (1T-MoS2) monolayers of similar phase. Both contributing monolayers have similar lattice structures, with a minimum lattice mismatch of 0.83 %, and have corrugation on both sides that can successfully retain foreign species at the vdW-gap. In the next step, interfacial engineering through Li-intercalation and layer-sliding was employed to modify physical properties of the vdWHS. It is the worth mentioning that a narrow bandgap of 0.102 eV (0.22 eV) has been observed in the unintercalated ZrO2/MoS2 vdWHS when employing PW-LDA (hybrid-functional). Li-intercalation and sliding process significantly influenced the electronic properties of the studied vdWHS. Furthermore, un-slided and fully-slided Li-intercalated vdWHS exhibit an increase in the vdW-gap by 3.78 % and 27.14 %, respectively, as compared to unintercalated vdWHS. To further understand the electrical behaviour at the interface of contributing monolayers, a comparative study has also been made for the variation in the planar average charge density difference, charge transfer, and interface dipole moment for unintercalated and intercalated vdWHS. In the unintercalated vdWHS, the calculated values of ΔQ and µ(z) provide evidence of significant charge transfer from 1T-ZrO2 to 1T-MoS2 before sliding, whereas in the fully-slided vdWHS, there is 80.11 % more charge transfer from 1T-MoS2 to 1T-ZrO2. Li-intercalation increases the magnitude of ΔQ (by 90.27 %) near 1T-MoS2, indicating a sufficient quantity of charge transfer from the 1T-MoS2 monolayer. The results of the anisotropic analysis show that the calculated in-plane and out-of-plane components of the real and imaginary parts of the dielectric function differ significantly. The optical absorption and energy losses of Li-intercalated vdWHS experience a substantial decrease of about 90 % and 50 %, respectively, as compared to unintercalated vdWHS. Our employed method promotes the notion that interfacial engineering through simultaneous layer-sliding and intercalation approach can be used to regulate and modify the physical properties of 2D insulator/metal based vdWHS.

Theoretical investigations of structural, electronic, magnetic, and optical properties of group V (X = V, Nb, Ta) added CeO2-X materials for optoelectronic applications.

CONTEXT: Depletion of natural resources, responsible for energy production, is a serious concern for researchers to develop alternate energy resources or materials. Scientists have proposed various energy materials which are based on semiconductors and their underlying physics. Cerium oxide (CeO2) is a versatile energy material which receives much attention owing to excellent photocatalytic, photonic, thermal stability, and optoelectronic applications. Even though CeO2 exhibited remarkable physical properties, but yet, they can be enhanced upon suitable doping. Focus on current research is to dope group V elements into CeO2 in order to enhance its electronic and optical response. The density of states (DOS) and band gaps of proposed materials are calculated, and significant improvement is noted after applying TB-mbj method. Optical absorption spectra of V/Nb/Ta-doped CeO2 show blueshift and decrease in reflectivity along with the presence of magnetism illustrate potential uses of these materials in future UV optoelectronics, spintronics, sensing, and energy harvesting devices. METHODS: This research is based on computational work carried using Wien2k code where PBE-GGA approximation is used to approximate exchange and correlation potentials. Supercells of vanadium/niobium/tantalum-doped CeO2 are constructed, and spin-polarized density of states (DOS) along with optical constant are calculated. TB-mbj method is used to bring improvements in DOS and band gaps of proposed materials. Iterations are conducted using convergence criterion, and non-relativistic calculations are performed.

A DFT approach to correlate the physical characteristics of novel chalcopyrites ASbN2(A = Li, Na) for green technology.

Semiconductor chalcopyrite compounds have been a subject of research interest due to their diverse range of physical properties that have captured the attention of scientists. In this ongoing research, we have examined the physical characteristics of LiSbN2 and NaSbN2 chalcopyrites using DFT. The modified Becke-Johnson (mBJ) potential is utilized for the computation of electronic structures. The stability is attained with negative formation energies and optimization curves. A bandgap of 2.60 eV in LiSbN2 and 3.15 eV in NaSbN2 has been achieved, which is further endorsed by the density of states. An in-depth analysis of the optical properties unveils the potential utility of LiSbN2 and NaSbN2 in various photovoltaic devices, attributed to its pronounced absorption in the UV spectrum. The transport characteristics are also assessed through various transport characteristics. The large electrical conductivity and ZT values for both chalcopyrite compounds are attained. Due to their remarkable capability to convert heat into electricity, these materials display potential for use in thermoelectric devices.

Parsimonious Topology Based on Frank-Kasper Polyhedra in Metal-Organic Frameworks.

A new topology previously unknown in metal-organic frameworks (MOFs) provides an important clue to uncovering a new series of polyhedral MOFs. We report a novel MOF crystallized in a parsimonious mep topology based on Frank-Kasper (FK) polyhedra. The distribution of angles in a tetrahedral arrangement (T-O-T) is crucial for the formation of FK polyhedra in mep topology. This finding led us to investigate the T-O-T angle distribution in related zeolites and zeolitic imidazolate frameworks (ZIFs). Unlike zeolites, it is extremely difficult to achieve high T-O-T angles in ZIFs, which prevents the formation of some FK topologies. Density functional theory (DFT) total energy calculations support a correlation between T-O-T angles and the feasibility of new tetrahedron-based FK frameworks. This result may lead to innovative ways of accessing new cellular topologies by simple chemical tweaking of T-O-T angles.

Co2YZ (Y= Cr, Nb, Ta, V and Z= Al, Ga) Heusler alloys under the effect of pressure and strain.

Full Heuslers alloys are a fascinating class of materials leading to many technological applications. These have been studied widely under ambient conditions. However, less attention been paid to study them under the effect of compression and strain. Here in this work Co2YZ (Y= Cr, Nb, Ta, V and Z = Al, Ga) Heusler alloys have been studied comprehensively under pressure variations. Calculated lattice constants are in reasonable agreement with the available data. It is determined that lattice constant deceases with the increase in tensile stress and increases by increasing pressure in reverse direction. Band profiles reveals the half metallic nature of the studied compounds. The bond length decreases while band gap increases in compressive strain. The compounds are found to be reflective in visible region, as characteristics of the metals. The magnetic moments reveal the half-mettalic ferromagnetic nature of the compounds.

Carbon-Heteroatom Bond Formation by an Ultrasonic Chemical Reaction for Energy Storage Systems.

The direct formation of CN and CO bonds from inert gases is essential for chemical/biological processes and energy storage systems. However, its application to carbon nanomaterials for improved energy storage remains technologically challenging. A simple and very fast method to form CN and CO bonds in reduced graphene oxide (RGO) and carbon nanotubes (CNTs) by an ultrasonic chemical reaction is described. Electrodes of nitrogen- or oxygen-doped RGO (N-RGO or O-RGO, respectively) are fabricated via the fixation between N2 or O2 carrier gas molecules and ultrasonically activated RGO. The materials exhibit much higher capacitance after doping (133, 284, and 74 F g-1 for O-RGO, N-RGO, and RGO, respectively). Furthermore, the doped 2D RGO and 1D CNT materials are prepared by layer-by-layer deposition using ultrasonic spray to form 3D porous electrodes. These electrodes demonstrate very high specific capacitances (62.8 mF cm-2 and 621 F g-1 at 10 mV s-1 for N-RGO/N-CNT at 1:1, v/v), high cycling stability, and structural flexibility.

Selective Tuning of a Particular Chemical Reaction on Surfaces through Electrical Resonance: An ab Initio Molecular Dynamics Study.

We used ab initio molecular dynamics (AIMD) to investigate the effect of a monochromatic oscillating electric field in resonance with a particular molecular vibration on surfaces. As a case study, AIMD simulations were carried out for hydroxyl functional groups on graphene. When the frequency of the applied field matches with the C-OH vibration frequency, the amplitude is monotonically amplified, leading to a complete desorption from the surface, overcoming the substantial barrier. This suggests the possibility of activating a particular bond without damaging the remaining surface. We extended this work to the case of the amination of sp(2)-bonded carbon surfaces and discussed the general perspective that, in general, an unfavorable chemical process can be activated by applying an external electric field with an appropriate resonance frequency.