State Energy Research Articles

Ir noble metal atoms/clusters on graphene support: Insights from aberration corrected-STEM and density functional theory

The interactions of Iridium (Ir) noble metal atoms/clusters (Ir NMAs/NMCs) with graphene are investigated due to their remarkable catalytic performance, resulting from the use of 100 % metal atoms compared to nanoparticle counterparts. Using scanning transmission electron microscopy (STEM), various forms of Ir dispersed on graphene were observed, including single atoms, dimers, and trimers clusters. The STEM data further revealed inter-atomic distances of 2.83 Å and 2.96 Å for dimers and trimers which were 20 % and 17 % larger than the numbers found through density functional theory (DFT) calculations. The DFT calculations further showed that the Dirac-cone of graphene at Ir NMAs/NMCs locations changes to metallic form due to the emergence of energy states at the Fermi level. This effect results in non-zero effective masses of charge carriers but enhances their density of states (DOS) by 2-fold which is believed to increase the energy absorption efficiency of graphene in the infra-red range of radiation.

Converging many-body perturbation theory for ab-initio nuclear structure: Brillouin-Wigner perturbation series for closed-shell nuclei

Convergence aspects of nuclear many-body perturbation theory for ground states of closed-shell nuclei are explored using a Brillouin-Wigner formulation with a new vertex function enabling high-order calculations. A general formalism for Hamiltonian partitioning and a convergence criterion for the perturbation series are proposed. Analytical derivations show that with optimal partitioning, the convergence criterion for ground states can always be satisfied. This feature attributes to the variational principle and does not depend on the choice of an internucleon interaction or a many-body basis. Numerical calculations of the ground state energies of He4 and O16 with Daejeon16 and a bare N3LO potential in both harmonic-oscillator and Hartree-Fock bases confirm this finding.

Theory of electric field effect on the optical properties of elliptical quantum wire

In the approximation of the effective mass, the electric field effect on the optical properties of the elliptical quantum wire (EQW) was investigated. In an elliptic coordinate system, exact solutions of the Schrödinger equation for an electron in an EQW with hard walls are obtained. The electron energy spectrum consists of even and odd energies states, whose wave functions are expressed through even and odd Mathieu functions of the first kind. Using these solutions, an orthonormal basis was constructed. The influence of the electric field perpendicular to the quantum wire and parallel to the ellipse’s major axis on the energies and oscillator strength of quantum electron transitions was calculated using the matrix method. It is shown that the ellipticity of the quantum wire leads to the removal of the degeneracy of the energy spectrum of quasiparticles since the energies of even and odd electronic states depend differently on the ratio of the EQW semi-axes. The electron’s ground state is the even state, which is nondegenerate because there is no corresponding odd state. The electric field has a greater effect on energy states with a lower value of the magnetic quantum number. As the electric field strength increases, the energies of even and odd states shift to the region of lower energies.

Exploring the potential of Mbenes in energy storage

MBene, a layered metal boride similar to MXene, has garnered significant attention in recent times. Nevertheless, there is still a lack of comprehensive understanding regarding their structure and properties, necessitating further research and investigation. In this study, theoretical calculations were employed first to study the binding energy, band structures and density of states of three MBenes, namely MoB, MgB2, and ZrB2, providing insights into their electronic characteristics. In addition, open circuit voltage (OCV) and adsorption energy were also conducted using the three MBenes as cathode materials for zinc ion batteries, indicating their low ion migration barrier and potential in energy storage application. Subsequently, MoB, MgB2, and ZrB2 were experimentally synthesized using etching or exfoliation method and utilized as cathode materials for zinc ion batteries. Results demonstrates that the specific capacity of MoB is 60 mAh g-1 at 0.1 A g-1. Systematic investigation including kinetics simulation and ex situ XRD suggests the cation insertion mechanism of the MoB electrodes. Building upon these findings, attempts were made to enhance the performance of MoB through the incorporation of 1 T-MoS2 composites, urea molecular intercalation. Notably, the modified composite exhibited a specific capacity exceeding 150 mAh g-1 at 0.1 A g-1, with a stable Coulombic efficiency of 100% after 100 cycles. This study provides novel directions and insights for the research of MBene in the context of aqueous zinc-ion batteries.

Absorption by cadmium sulfide nanocrystals in the ultraviolet spectral ranges

Within the framework of the effective mass approximation, the energy of the ground state of an electron-hole pair was obtained by the variational method as a function of the radius of the nanocrystal of cadmium sulfide. Determined that the absorption peaks of the nanosystem are caused by interband transitions of electrons from quantum-confined energy levels, located in the valence band of a colloidal nanocrystal of cadmium sulfide, to quantum-confined energy levels, located in the conduction band of CdS nanocrystal.

Development of Parallel On-the-Fly Crystal Algorithm for Global Exploration of Conical Intersection Seam Space.

Conical intersection (CI) seams are configuration spaces of a molecular system where two or more (spin) adiabatic electronic states are degenerate in energy. They play essential roles in photochemistry because nonradiative decays often occur near the minima of the seam, i.e., the minimum energy CIs (MECIs). Thus, it is important to explore the CI seams and discover the MECIs. Although various approaches exist for CI seam exploration, most of them are local in nature, requiring reasonable initial guesses of geometries and nuclear gradients during the search. Global search algorithms, on the other hand, are powerful because they can fully sample the configurational space and locate important MECIs missed by local algorithms. However, global algorithms are often computationally expensive for large systems due to their poor scalability with respect to the number of degrees of freedom. To overcome this challenge, we develop the parallel on-the-fly Crystal algorithm to globally explore the CI seam space, taking advantage of its superior scaling behavior. Specifically, Crystal is coupled with on-the-fly evaluations of the excited and ground state energies using multireference electronic structure methods. Meanwhile, the algorithm is parallelized to further boost its computational efficiency. The effectiveness of this new algorithm is tested for three types of molecular photoswitches of significant importance in material and biomedical sciences: photostatin (PST), stilbene, and butadiene. A rudimentary implementation of the algorithm is applied to PST and stilbene, resulting in the discovery of all previously identified MECIs and several new ones. A refined version of the algorithm, combined with a systematic clustering technique, is applied to butadiene, resulting in the identification of an unprecedented number of energetically accessible MECIs. The results demonstrate that the parallel on-the-fly Crystal algorithm is a powerful tool for automated global CI seam exploration.

Ultrafast Dynamics of Self-Trapped Excitons in Cs2AgInCl6:Al3+ Double Perovskite Nanocrystals.

It is a huge challenge to increase the photoluminescence (PL) of lead-free halide perovskites, and understanding the mechanism behind exciton dynamics can provide a valuable solution. Herein, we achieved enhanced broad-band emission at ambient conditions in Cs2AgInCl6 by tuning self-trapped excitons (STEs) through Al3+ doping. Cryogenic measurements showed an inhomogeneous nature of STE emission due to the presence of defect states and is subject to thermal quenching. An increased Huang-Rhys factor (S-factor) resulted in better electron-phonon coupling and high-density STE states post Al3+ doping. Femtosecond transient absorption (fs-TA) results provided insights into the distribution dynamics of excitons, which occurs through gradient energy levels from free excitons (FE) to STEs, where each STE state potentially possesses higher quantized energy states. Overall, this study aims to comprehend the origins of self-trapping and decay of STEs in Cs2AgInCl6:Al3+ and emphasizes the potential of compositional engineering to mitigate self-trapping in this material.

Reaction mechanisms for methyl isocyanate (CH3NCO) gas-phase degradation

Methyl isocyanate (MIC) is a toxic chemical found in many commercial, industrial, and agricultural processes, and was the primary chemical involved in the Bhopal, India disaster of 1984. The atmospheric environmental chemical reactivity of MIC is relatively unknown with only proposed reaction channels, mainly involving OH-initiated reactions. The gas-phase degradation reaction pathways of MIC and its primary product, formyl isocyanate (FIC), were investigated with quantum mechanical (QM) calculations to assess the fate of the toxic chemical and its primary transformation products. Transition state energy barriers and reaction energetics were evaluated for thermolysis/pyrolysis-like reactions and bimolecular reactions initiated by relevant radicals (•OH and Cl•) to evaluate the potential energy surfaces and identify the primary reaction pathways and products. Thermolysis/pyrolysis of MIC requires high energy to initiate N-CH3 and C-H bond dissociation and is unlikely to dissociate except under extreme conditions. Bimolecular radical addition and H-abstraction reaction pathways are deemed the most kinetically and thermodynamically favorable mechanisms. The primary transformation products of MIC were identified as FIC, methylcarbamic acid, isocyanic acid (isocyanate radical), and carbon dioxide. The results of this work inform the gas-phase reaction channels of MIC and FIC reactivity and identify transformation products under various reaction conditions.

Classifying Multiparticle Entanglement with Passive State Energies

AbstractThermodynamics as a fundamental branch of physics examines the relationships between heat, work, and energy. The maximum energy extraction can be characterized by using the passive states that have no extracted energy under any cyclic unitary process. In this paper, the focus is on the concept of marginal passive state energy and derive polygon inequalities for multi‐qubit entangled pure states. It is shown that the marginal passive state energies collectively form a convex polytope for each class of quantum states that are equivalent under SLOCC. Multipartite passive state energy criteria is introduced to classify multipartite entanglement under SLOCC. The present result provides a thermodynamic method to witness multipartite entanglement.

Hydrogen-like impurities in Si and Ge quantum dots in connection with 5 nm and beyond metal-oxide-semiconductor technologies

The industrial drive towards smaller semiconductor devices is at less than 10 nano-meters. In the next few years a three-dimensional quantum confined device structure is expected. We have studied the electronic structure of hydrogen-like donor impurities in Si and Ge quantum dots with varied shape of the confinement potential. These calculations are carried out within the Density-Functional-Effective-Mass Theory (DF-EMT). We have paid particular attention to the electron-electron interaction energy in a negative charge state of the donor impurity. The effect of electron correlation on the binding energy has been explored. In addition to these, we show that the second order correction to the ground state energy obtained through perturbative approach agrees well with the DF-EMT based numerical results, down to very small sizes of the quantum dots when the depth of the confinement is moderate or small. A non-monotonic shallow-deep transition of the binding energy of neutral and charged donors of hydrogen-like impurities is expected to occur with the reduction in the size of the quantum dot. A similar effect is expected for hydrogen-like acceptor impurities as well. Furthermore, the optical gap also shows non-monotonic shallow-deep behaviour with the quantum dot size reduction. Deepening of shallow donor or acceptor level implies that the carriers will freeze out at small sizes of the dot. We believe this is quite important in the context of metal-oxide-semiconductor (MOS) devices beyond 5 nm technologies, based on Si, Ge or a combination (SiGe). We also point out possible variabilities in the binding energy of donors and acceptors if there are variations in the size of host quantum dots in a large assembly of devices in future integrated circuits. This will lead to the variabilities in the characteristics from device to device. These results should be incorporated in the Technology Computer Aided Design (TCAD) simulation of less than or equal to 5 nm MOS devices.

Enjoyment and Affective Responses to Moderate and High-Intensity Exercise: A Randomized Controlled Trial in Individuals with Subsyndromal PTSD.

This crossover randomized controlled trial examined the acute psychological effects of a bout of moderate-intensity continuous aerobic exercise (MICE) and a bout of high-intensity functional exercise (HIFE), relative to a no-exercise sedentary control (SED), in participants (N = 21; 15 f; 24.7 ± 9.3 years) with subsyndromal post-traumatic stress disorder (PTSD). Affective state (Energy, Tiredness, Tension, Calmness) was assessed before (Pre), immediately after (Post 0), 20-min after (Post 20), and 40-min after (Post 40) each condition. Affective valence was assessed during each condition, and exercise enjoyment was assessed at Post 0. Enjoyment was significantly greater following HIFE and MICE relative to SED. Energy was significantly increased Post 0 HIFE and MICE but decreased Post 0 SED. Tension was reduced following all conditions and was significantly lower at Post 40 relative to Pre for HIFE, MICE, and SED. Tiredness was significantly reduced at Post 40 relative to Pre following MICE only, while Calmness was significantly lower at Post 40 relative to Pre following MICE and SED. Overall, both exercise conditions were enjoyed to a greater extent than the control, but MICE may provide greater psychological benefits with respect to Calmness and Tiredness. This study is among the first to assess acute changes in affective states relative to various exercise modes in individuals living with subsyndromal PTSD.

Ultrafast Laser Processing of 2D Materials: Novel Routes to Advanced Devices.

Ultrafast laser processing has emerged as a versatile technique for modifying materials and introducing novel functionalities. Over the past decade, this method has demonstrated remarkable advantages in the manipulation of 2D layered materials, including synthesis, structuring, functionalization, and local patterning. Unlike continuous-wave and long-pulsed optical methods, ultrafast lasers offer a solution for thermal heating issues. Nonlinear interactions between ultrafast laser pulses and the atomic lattice of 2D materials substantially influence their chemical and physical properties. This paper highlights the transformative role of ultrafast laser pulses in maskless green technology, enabling subtractive, and additive processes that unveil ways for advanced devices. Utilizing the synergetic effect between the energy states within the atomic layers and ultrafast laser irradiation, it is feasible to achieve unprecedented resolutions down to several nanometers. Recent advancements are discussed in functionalization, doping, atomic reconstruction, phase transformation, and 2D and 3D micro- and nanopatterning. A forward-looking perspective on a wide array of applications of 2D materials, along with device fabrication featuring novel physical and chemical properties through direct ultrafast laser writing, is also provided.

Recent Progress of Ion-Modified TiO2 for Enhanced Photocatalytic Hydrogen Production.

Harnessing solar energy to produce hydrogen through semiconductor-mediated photocatalytic water splitting is a promising avenue to address the challenges of energy scarcity and environmental degradation. Ever since Fujishima and Honda's groundbreaking work in photocatalytic water splitting, titanium dioxide (TiO2) has garnered significant interest as a semiconductor photocatalyst, prized for its non-toxicity, affordability, superior photocatalytic activity, and robust chemical stability. Nonetheless, the efficacy of solar energy conversion is hampered by TiO2's wide bandgap and the swift recombination of photogenerated carriers. In pursuit of enhancing TiO2's photocatalytic prowess, a panoply of modification techniques has been explored over recent years. This work provides an extensive review of the strategies employed to augment TiO2's performance in photocatalytic hydrogen production, with a special emphasis on foreign dopant incorporation. Firstly, we delve into metal doping as a key tactic to boost TiO2's capacity for efficient hydrogen generation via water splitting. We elaborate on the premise that metal doping introduces discrete energy states within TiO2's bandgap, thereby elevating its visible light photocatalytic activity. Following that, we evaluate the role of metal nanoparticles in modifying TiO2, hailed as one of the most effective strategies. Metal nanoparticles, serving as both photosensitizers and co-catalysts, display a pronounced affinity for visible light absorption and enhance the segregation and conveyance of photogenerated charge carriers, leading to remarkable photocatalytic outcomes. Furthermore, we consolidate perspectives on the nonmetal doping of TiO2, which tailors the material to harness visible light more efficiently and bolsters the separation and transfer of photogenerated carriers. The incorporation of various anions is summarized for their potential to propel TiO2's photocatalytic capabilities. This review aspires to compile contemporary insights on ion-doped TiO2, propelling the efficacy of photocatalytic hydrogen evolution and anticipating forthcoming advancements. Our work aims to furnish an informative scaffold for crafting advanced TiO2-based photocatalysts tailored for water-splitting applications.

International Legal Approach to Understanding Energy Diplomacy

INTRODUCTION. The relevance of the research topic is determined, firstly, by the increasing importance of energy diplomacy for solving modern problems arising in the field of international energy cooperation, and secondly, by the significance of studying the problems of energy diplomacy from the point of view of the science of international law. Despite the fact that energy diplomacy is being formed and realizing its potential in the international legal environment, it is not given adequate attention to its role in the legal literature, including in scientific works on international law, which, in turn, looks like a gap in international legal science. The purpose of the work is to substantiate the international legal concept of energy diplomacy, to identify its connection with the classical model of diplomacy and at the same time specific, to objectively identify the main directions of the relationship between energy diplomacy and international law.MATERIALS AND METHODS. When writing the work, scientific works related to the topic, international treaties and documents of international law, acts of national legislation of states are analyzed. General scientific and special methods of cognition, including comparative legal and formal legal, were used as a research method.RESEARCH RESULTS. Energy diplomacy is derived from the “classical” model of diplomacy. There are various interpretations of diplomacy, focusing on its various aspects and manifestations. The article substantiates the understanding of diplomacy as a means of implementing the state’s foreign policy through the activities of special entities (bodies of foreign relations) using non-military techniques and methods in accordance with international law. The evolution of diplomacy and the emergence of its new forms are traced, their specificity and international legal component are noted. Taking into account the specifics of energy, international energy cooperation, their legal support based on the potential of international and national law, the independent nature of energy diplomacy, its increasing role in modern conditions is substantiated. The specific features of energy diplomacy are identified and its concept is proposed, taking into account the international legal component. In modern conditions, full-fledged regulatory and institutional legal foundations of the EU’s foreign energy policy and energy diplomacy have not developed. It is noted that the legitimacy of unilateral restrictive measures applied in energy diplomacy by a number of states is indisputable from the point of view of international law. The main directions of the relationship between energy diplomacy and international law are outlined in detail, options for legitimizing the national interests of states in the energy sector based on the potential of international law are highlighted.DISCUSSION AND CONCLUSIONS. The main conclusions of the study are as follows. Firstly, energy diplomacy is a new functional area of diplomatic activity. It has a single essence with “classical” diplomacy (to serve as a means of implementing foreign policy, in accordance with international law) and, at the same time, is characterized by a number of features derived from the energy sector and energy law (a special focus on the implementation of the goals and objectives of the state's foreign energy policy, the participation of energy departments in it and the connection of energy companies, methods used in it). Secondly, energy diplomacy and international law in the process of their development and functioning are mutually linked and have a reciprocal influence. International law, firstly, defines the legal framework and forms of implementation of energy diplomacy (as well as diplomatic activity in general), and secondly, plays a decisive role in legitimizing the national interests of states in the field of foreign energy policy carried out through energy diplomacy. In turn, energy diplomacy, relying on the potential of international law, contributes to ensuring energy security (national and international) and, thereby, to maintaining the international energy order. In general, energy diplomacy influences the process of creation and operation of international law norms and contributes to the development of international law.

Computational Analysis of Low Overpotential Ammonia Oxidation by Metal-Metal Bonded Ruthenium Catalysts, and Predictions for Related Osmium Catalysts.

The catalyzed electrochemical oxidation of ammonia to nitrogen (AOR) is an important fuel-cell half-reaction that underpins a future nitrogen-based energy economy. Our laboratory has reported spontaneous chemical and electrochemical oxidation of ammonia to dinitrogen via reaction of ammonia with the metal-metal bonded diruthenium complex Ru2(chp)4OTf (chp- = 2-chloro-6-hydroxypyridinate, TfO- = trifluoromethanesulfonate). This complex facilitates electrocatalytic ammonia oxidation at mild applied potentials of -255 mV vs ferrocene, which is the [Ru2(chp)4(NH3)]0/+ redox potential. We now report a comprehensive computational investigation of possible mechanisms for this reaction and electronic structure analysis of key intermediates therein. We extend this analysis to proposed second-generation electrocatalysts bearing structurally similar fhp and hmp (2-fluoro-6-hydroxypyridinate and 2-hydroxy-6-methylpyridinate, respectively) equatorial ligands, and we further expand this study from Ru2 to analogous Os2 cores. Predicted M24+/5+ redox potentials, which we expect to correlate with experimental AOR overpotential, depend strongly on the identity of the metal center, and to a lesser degree on the nature of the equatorial supporting ligand. Os2 complexes are easier to oxidize than analogous Ru2 complexes by ∼640 mV, on average. In contrast to mono-Ru catalysts, which oxidize ammonia via a rate-limiting activation of the strong N-H bond, we find lowest-energy reaction pathways for Ru2 and Os2 complexes that involve direct N-N bond formation onto electrophilic intermediates having terminal amido, imido, or nitrido groups. While transition state energies for Os2 complexes are high, those for Ru2 complexes are moderate and notably lower than those for mono-Ru complexes. We attribute these lower barriers to enhanced electrophilicity of the Ru2 intermediates, which is a consequence of their metal-metal bonded structure. Os2 intermediates are found to be, surprisingly, less electrophilic, and we suggest that Os2 complexes may require access to oxidation states higher than Os25+ in order to perform AOR at reasonable reaction rates.

Computational study on the adsorption and mechanisms of the hydrogenation of N-Cbz-protected glycine, alanine, valine, and phenylalanine on palladium, Pd (1 0 0), surface

Materials Studio (MS) is powerful software (with various useful tools) that is designed for simulating and modeling of different molecules and materials in computational chemistry, cheminformatics, bioinformatics, and etc. Density functional theory (DFT), with periodic slab model, is one of the most applied theoretical approaches for understanding surface-adsorbate interaction strength and reactivity. In this study, DFT method have been used via Materials Studio software to study the adsorption (at T = 298.15 K, 308.15 K, and 318.15 K) and hydrogenation (at constant temperature T = 298.15 K) of four series of N-Cbz-protected amino acids (Cbz-aa's include N-Cbz-l-phenylalanine, Cbz-pheala, N-Cbz-l-valine, Cbz-val, N-Cbz-l-alanine, Cbz-ala, and N-Cbz-l-glycine, Cbz-gly) on palladium, Pd (1 0 0), surface. During calculations of this study, a cell with periodic boundary conditions was constructed and each Cbz-aa was located and studied in this cell. For calculations of the hydrogenation of Cbz-aa's on Pd (1 0 0) surface at constant temperature, Materials Studio QMERA (combined QM/MM methods) has been employed. For calculations of the adsorption of Cbz-aa's on Pd (1 0 0) surface at different temperatures, the Materials Studio Sorption module has been applied. In the adsorption processes, average adsorption isosteric heat (Qst) and average total energy or overall system energies (Etotal) were extracted. In the hydrogenation processes, the energy of reaction (ΔH) and energy barrier (Eb) were obtained. In this study, three different mechanisms (mechanism 1: M1, mechanism 2: M2, and mechanism 3: M3) were suggested for the hydrogenation of each Cbz-aa on Pd (1 0 0) surface. We suggested these mechanisms based on the sites (atoms) that are probable for adding two hydrogen atoms (from H2) as well as the strength of bonds that should be broken for adding two hydrogen atoms (from H2). For these three mechanisms, the energy of reaction (ΔH), transition state, and energy barrier (Eb) were calculated. The obtained values of ΔH show that mechanism 3 (M3) provides the most facile mechanism to perform hydrogenation of Cbz-aa's on Pd (1 0 0) surface. Further, the negative sign of ΔH for M3 shows that mechanism 3 is an exothermic reaction in the case of all our studied Cbz-aa's. Hydrogenation and adsorption data show that Qst very slowly decreases and Etotal very slowly increases when temperature increases. Also, molecular weight and stereochemistry of Cbz-aa's molecules are two important factors that affect the values of Qst, Etotal, Eb, and ΔH.

Negative single-trace TT¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ T\\overline{T} $$\\end{document} holography holography versus de Sitter

In single-trace TT¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ T\\overline{T} $$\\end{document} holography, for the negative sign of the deformation, the geometries dual to high energy states consist of a singular UV wall that separates black strings in the IR from an asymptotically linear dilaton spacetime. In the hologram, the black strings amount to states in a symmetric product of TT¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ T\\overline{T} $$\\end{document} deformed CFT2, whose energy and momentum are split equally among the different blocks. The properties of this holographic duality have intriguing similarities with the proposed principles of de Sitter holography. In this note, the analogy between the two is presented. In particular, as the horizon location approaches the UV wall, one obtains a state of maximum finite entropy and infinite temperature. On the other hand, the bulk temperature of the geometry obtained in the limit is small. These properties are identical to those proposed in empty de Sitter holography.

Optoelectronic and transport properties of Lead-Free halide based Na2AgTlZ6 (Z = Cl, Br, I) double perovskites for energy harvesting applications

The bandgap engineering and deliberate band edge manipulation of perovskites make them potential candidates for the photovoltaic industry. Here we theoretically investigate the structure, density of states, and photovoltaic and thermoelectric characteristics of Na2AgTlZ6 (Z = Cl, Br, I) using WIEN2k code. The incorporation of Br and I at the Cl site caused the increase in lattice constant which leads to the decrease in bulk modulus and Debye temperature. The computed values of Poisson (<0.26) and Pugh (<1.75) ratio verified their brittle nature. The bandgap analysis reveals direct bandgap nature and bandgap value lie in the visible region for parent composition and infrared and far infrared when Cl is replaced with Br and I. The density of state plots uncovers the shifting of energy states in valence and conduction bands towards the Fermi level with the increasing number of electrons in the halogens. The increase in the value of dielectric constant, refractive index, and shifting of peaks towards lower energy value is witnessed with atomic number of halogen atoms. The viability of these compositions for thermoelectric devices is further confirmed when electrical conductivity and Seebeck coefficient dependent Figure of merit and power factor are evaluated in the temperature range of 200–800 K. In addition, the anisotropic nature of studied compositions is explored through the computation of the modulus of elasticity including Young’s modulus, Shear modulus in addition to compressibility, and Poisson’s ratio.

First principles study of transition metal (TM = Sc, Ti, V, Cr, Mn) doped penta-BAs5 monolayer for adsorption of CO, NH3, NO, SO2

In this paper, the adsorption capacity of intrinsic penta-BAs5 monolayer on CO, NH3, NO, SO2 and the effect of transition metal doping on gas sensing characteristics are systematically studied by first-principles calculations. Adsorption energy, recovery time, band structure, charge transfer and density of states (DOS) are investigated. The electronic properties and sensing mechanisms under different adsorption systems are expounded. The results showed that the intrinsic penta-BAs5 monolayer had the strongest adsorption capacity for NO and weak sensitivity to CO, NH3 and SO2, which shown strong gas selectivity. Moreover, the recovery time of NO at 380 k was 3.93 s, which was more inclined to be desorption at high temperature. In addition, Sc and Ti doping could selectively improve the adsorption capacity of the intrinsic penta-BAs5 monolayer. The charge transfer of SO2-Sc-BAs5 and CO-Ti-BAs5 were increased by 6.78 and 10.33 times compared with those before doping. The band structure and DOS show that Ti atom and CO have orbital hybridization, which improved the interaction between gases and penta-BAs5. Therefore, intrinsic penta-BAs5, Sc-BAs5 and Ti-BAs5 are suitable for gas sensing and toxic gas monitoring, and have broad application prospects.

Isotropic compact stars admitting Heintzmann solution in Rastall gravity

This paper is devoted to observe the physical attributes of static spherically symmetric isotropic compact stellar candidates in the context of Rastall theory of gravity. In order to inspect the structural composition of compact objects, the Heintzmann ansatz is taken into account. The unknown parameters associated with Heintzmann ansatz are evaluated through matching conditions with derived values of radii and masses of some specific star models. The consistency of the adopted ansatz is analyzed via graphical interpretation of matter variables, equation of state parameter, mass components, energy constraints, causality condition, stellar equation and adiabatic index for several choices of Rastall parameter. It is observed that the stars under consideration manifest stable structures corresponding to Heintzmann ansatz in this framework. Moreover, it is shown that for vanishing Rastall coupling parameter, the standard outcomes of general relativity can be retrieved.