Exchange Energy Research Articles

Effect of the external electric fields on the polarization and vibrational spectrum of 1-ethyl-3-methylimidazolium bis(trifluormethylsulfonyl)imide on graphene surface

Ionic liquids, emerging as innovative solvents for energy harvesting, necessitate a comprehensive understanding of their structural characteristics at the graphene-ionic liquid interface. This work delves into the effects of external electric fields (EEFs) on the polarization and vibrational spectrum of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][NTf2]) on a graphene surface, employing density functional theory calculations. The analysis reveals that the geometrical configuration and stability of functional groups within the graphene-[Emim][NTf2] system are influenced by both the direction and intensity of the applied EEF. Notably, the threshold EEF strength required for dissociation varies based on the structural configuration of the anion. The electronic energy, dipole moment, and polarization rate under varying EEF conditions have been quantitatively assessed, providing insights into their EEF-dependent behaviors. Utilizing the independent gradient model approach, the inter-ion interactions, such as hydrogen bonding and van der Waals forces, under the influence of EEFs were analyzed, and how these interactions evolve with changes in the direction and intensity of the EEFs were also explored. Furthermore, the vibrational spectrum of [Emim][NTf2] on the graphene surface, spanning a range of 10–3500 cm−1, was meticulously calculated to systematically investigate the impact of the EEF on the vibrational spectra of the graphene-[Emim][NTf2] system. A key finding of this work is the distinct shifts in the vibrational peaks of the cis and trans isomers of [NTf2]− on the graphene surface, which can be attributed to differences in their exchange energies. Specifically, the exchange energy for the cis isomer of [NTf2]− is measured at 107.43 kJ∙mol−1, in contrast to 98.51 kJ∙mol−1 for the trans isomer.

Electronic properties and quantitative mapping of magnetic moments of rare-earth hard magnet SmCo5: First principles computations and inelastic scattering

Looking at the limitations of neutron spectroscopy in exploring properties of rare earth hard magnet SmCo5, inelastic scattering for charge and magnetic Compton profiles are attempted. The experimental momentum densities using 661.65 keV γ-ray energy are compared with the theoretical Compton profiles (CPs) deduced using linear combination of atomic orbitals (LCAO) with different exchange and correlation potentials and also spin polarized relativistic Korringa-Kohn-Rostoker (SPR-KKR) calculations. The anisotropies in the computed CPs, along the principal directions, show high momentum densities along the c-axis [00.1] of SmCo5 than [10.0] and [11.0] directions. An overall better agreement of CP computed using LCAO-GGA and that from experiment is observed which shows more appropriateness of GGA-PBE scheme for the exchange and correlation energies for SmCo5. The small value of charge transfer from Sm → Co and positive value of overlap Mulliken population dictate dominance of covalent bonding in SmCo5. Moreover, available experimental data on c-axis oriented magnetic CP (MCP) of SmCo5 have been compared with the present SPR-KKR calculations. It is seen that present SPR-KKR based MCP is in resemblance with the available experimental MCP. A decomposition of experimental MCP in to its constituent profiles depict that the spin momentum of Co and Sm are aligned anti-parallel while the diffuse contribution aligns opposite to the absolute spin moment. Comparison of amplitude and direction of site specific spin moments in SmCo5 is made with the present SPR-KKR and available experimental and theoretical data.

Polymeric dichlorido-bridged copper(II) offset stacked dimer coordination compounds and molecular spin stairs

A family of oxygen coordinated dichlorido-bridged n-X-2-pyridone (1, n = 3, X = Cl; 2, n = 3, X = Br; 3, n = 4, X = Cl; 4, n = 4, X = Br; 5, n = 5, X = Cl; 6, n = 5, X = Br) Cu(II) offset stacked dimer compounds, denoted molecular spin stairs, have been prepared and analyzed by single-crystal X-ray diffraction (1–4), powder X-ray diffraction (1–6), and variable temperature magnetic susceptibility measurements (1–6). Ferromagnetism is dominant in all compounds with a weaker antiferromagnetic exchange present in 1–4. The ferromagnetic exchange correlates to increased twist angles which are defined by the extent of the tetrahedral distortion of the copper coordination sphere and the identity of the halogen on the ring. The compounds were qualitatively fit to a ferromagnetic Heisenberg chain model with a Curie-Weiss interchain correction. The general Hamiltonian used is of the form H = − J ∑ S 1 S 2 . The ratio of exchange energies denoted α ( α = J FM | J AFM | ) ranges between 2.6 and 4.7. This family of compounds constitutes possible S = ½ Haldane-like materials.

Unraveling Halogen Role in Two-Step Solution Growth of Organic-Inorganic Hybrid Mixed-Halide Perovskites: Guidelines of Fabricating Single-Phase Perovskites with Predictable Stoichiometry.

The challenge faced in optoelectronic applications of halide perovskites is their degradation. Minimizing material imperfections is critical to averting cascade degradation processes. Identifying causes of such imperfections is, however, hindered by mystified growth processes and is particularly urgent for mixed-halide perovskites because of inhomogeneity in growth and phase segregation under stresses. To unravel two-step solution growth of MAPbBr x I3-x , we monitored the evolution of Br composition and found that the construction of perovskite lattice is contributed by iodine from PbI2 substrate and Br from MABr solution with a 1:1 ratio rather than a 2:1 ratio originally thought. Kinetic analysis based on a derived three-stage model extracted activation energies of perovskite construction and anion exchange. This model is applicable to the growth of PbI2 reacting with a mixed solution of MABr and MAI. Two guidelines of fabricating single-phase MAPbBr x I3-x with predictable stoichiometry thus developed help strategizing protocols to reproducibly fabricate mixed-halide perovskite films tailored to specific optoelectronic applications.

Extant linkages between Shanghai crude oil and US energy futures: Insights from spillovers of higher-order moments

This study is epicentral to analyzing the impact of futures volatility on portfolio and risk management, as extant literature indicates the challenges of using economic variables that fall short of forecasting volatility beyond lagged values. Further, higher moments may be better adaptive to signaling distress during market upheavals. This paper sources data from Bloomberg from March 26, 2018–April 28, 2023, to examine the dynamic spillovers of higher moments among Shanghai International Energy Exchange and US energy futures contracts by constructing realized skewness and kurtosis. Using nonlinear techniques of mutual information and time-varying vector autoregression (TVP-VAR), we show that realized skewness and kurtosis offer significant information on spillover transmission between the two futures markets, primarily through the crises of COVID-19 and the Russia and Ukraine war. Further, we identify that the risks embedded in these future contracts have increased significantly. Our results have important implications for policymakers, investors, and risk managers.

Sub-nanosecond magnetic vortex reversal induced by localized resonant strain field in doped nanomagnets

The strain-induced magnetic vortex dynamics in nanomagnets with ring-shaped impurities are investigated by means of micromagnetic simulations. It is found that the type and location of impurities can modulate the strain-stimulated spin wave spectrum of the magnetic vortex. Compared with pure nanomagnets without doping, the scattering impurities make the eigenfrequency of nanomagnets higher, while the pinning impurities lead to lower eigenfrequency. Moreover, the spin wave oscillation amplitude in a doped nanomagnet is strengthened by the gradient of exchange energy at the interface between the impurity ring and nanomagnet. The magnetic vortex polarity in a nanomagnet with specific doping schemes can be reversed in a sub-nanosecond scale by a localized resonant strain signal. Besides the switching efficiency improvement, the threshold stress of sub-nanosecond polarity reversal in nanomagnets with specific doping schemes is also reduced compared to the counterpart of nanomagnets without impurities. These results indicate that doping engineering of nanomagnets is a significant method to achieve straintronic devices with higher operating frequency and lower energy consumption.

Investigation of stabilization and survival of skyrmion vortices in the presence of magnetic field disorder in two-dimensional lattices: a case study for Janus dichalcogenides

Due to the lack of inversion symmetry, very large Dzyaloshinskii–Moriya interaction (DMI) has been reported for a series of Janus monolayers of manganese dichalcogenides within the framework of first-principles calculations (Liang et al 2020 Phys. Rev. B 101 184401). However, from the viewpoint of potential applications, the current ongoing research mainly focuses on the magnetism in pristine two-dimensional (2D) materials exhibiting non-zero DMI, and the effects of disorder in such systems remain an open problem since the influence of randomness may create some drastic effects on the magnetism of low dimensional systems. Here, we present Monte Carlo simulation results regarding the magnetic properties of a 2D manganese based Janus dichalcogenide material MnSTe in the presence of quenched random magnetic fields where the local field variables have been sampled from a Gaussian distribution. For the selected benchmark material, it has been found that the magnetic skyrmion vortexes emerging at (10 K, 3 T) may survive in the presence of weak and moderate quenched randomness, which is important from the viewpoint of technological applications. In both the pristine and random field cases, the stabilization of magnetic skyrmions are achieved by the major contribution of the ferromagnetic exchange energy to the total energy of the system, and the materials exhibiting large DMI/exchange ratios may exhibit resilient magnetic skyrmion vortexes in the presence of weak and moderate amount of randomness.

Balance between FeIV-NiIV synergy and Lattice Oxygen Contribution for Accelerating Water Oxidation.

Hydrogen obtained from electrochemical water splitting is the most promising clean energy carrier, which is hindered by the sluggish kinetics of the oxygen evolution reaction (OER). Thus, the development of an efficient OER electrocatalyst using nonprecious 3d transition elements is desirable. Multielement synergistic effect and lattice oxygen oxidation are two well-known mechanisms to enhance the OER activity of catalysts. The latter is generally related to the high valence state of 3d transition elements leading to structural destabilization under the OER condition. We have found that Al doping in nanosheet Ni-Fe hydroxide exhibits 2-fold advantage: (1) a strong enhanced OER activity from 277 mV to 238 mV at 10 mA cm-2 as the Ni valence state increases from Ni3.58+ to Ni3.79+ observed from in situ X-ray absorption spectra. (2) Operational stability is strengthened, while weakness is expected since the increased NiIV content with 3d8L2 (L denotes O 2p hole) would lead to structural instability. This contradiction is attributed to a reduced lattice oxygen contribution to the OER upon Al doping, as verified through in situ Raman spectroscopy, while the enhanced OER activity is interpreted as an enormous gain in exchange energy of FeIV-NiIV, facilitated by their intersite hopping. This study reveals a mechanism of Fe-Ni synergy effect to enhance OER activity and simultaneously to strengthen operational stability by suppressing the contribution of lattice oxygen.

Sustainable CO2 Refrigeration System for Fish Cold Storage Facility Using a Renewable Integrated System with Solar, Wind and Tidal Energy for Cape Verde—Analyzing Scenarios

This study compares four feasible alternative solutions for an integrated cold storage system in the city of Tarrafal, Santiago, Cape Verde. Integrated systems using grid electricity are compared with autonomous systems generating electrical energy from renewable sources, alongside various types of refrigeration facility systems. Its objective is to assess the energy efficiency, financial feasibility, and environmental impact across four scenarios. Scenario 1 utilizes two R134a refrigeration units powered by the public grid. Scenario 2 employs a transcritical R744 (CO2) system using grid electricity. Scenario 3 incorporates R744 and autonomous renewable energy. Scenario 4 employs R744 for refrigeration with seawater heat exchange and autonomous renewable energy sources. The findings favor Scenario 4, emitting 15,882 kg CO2 eq with a 5-year return on investment. Autonomous electricity production in this scenario reduces emissions by 95%. Despite an initial cost of EUR 769,172.00, Scenario 3 demonstrates financial viability, contributing to energy sustainability. This autonomous production reduces emissions by 360,697 kg CO2 compared to conventional systems, highlighting the positive impact of local renewable energy integration.

Impact of MCT Oil and Caffeine on Substrate Metabolism during Submaximal Exercise

Introduction: Recent research has suggested that medium-chain triglyceride (MCT) supplementation may increase fat oxidation (FatOx) during aerobic exercise, sparing muscle glycogen and, perhaps, enhancing performance. As both MCT and caffeine (CAF) are theorized to elicit these effects, this pilot study’s purpose was to compare the physiological responses of their combined supplementation during submaximal cycling exercise. Methods: Eight aerobically trained males (mean±SD; age 23.6±4.4 years; body mass 82.3±15.8 kg; height 180.9±8.7 cm) completed one aerobic capacity (VO2peak) test and three 45-min exercise trials at 60% VO2peak. Blinded and counterbalanced, one-hour prior to each trial, participants consumed: MCT+CAF (20 mL + 100 mg), long-chain triglycerides (LCT)+CAF (40 mL + 100 mg), or CAF (100 mg). Oxygen consumption (VO2), carbon dioxide output (VCO2), and minute ventilation (VE) were measured, subsequently calculating respiratory exchange ratio (RER), energy expenditure (EE), carbohydrate oxidation (CarbOx), and FatOx. Results: No significant differences between conditions were observed for average VO2 (p=0.474; η2=0.101), VE (p=0.323; η2=0.149), (RER (p=0.323; η2=0.149), EE (p=0.474; η2=0.101), CarbOx (p=0.274; η2=0.169), or FatOx (p=0.478; η2=0.100) or for total EE (p=0.474; η2=0.101), CarbOx (p=0.274; η2=0.169), or FatOx (p=0.478; η2=0.100). Conclusions: Co-ingestion of MCT+CAF didn’t produce any significantly different physiological responses compared to co-ingestion of LCT+CAF or the CAF control.

Multilayer Metamaterials with Ferromagnetic Domains Separated by Antiferromagnetic Domain Walls

AbstractMagnetic nano‐objects possess great potential for more efficient data processing, storage, and neuromorphic‐type applications. Using high perpendicular magnetic anisotropy synthetic antiferromagnets in the form of multilayer‐based metamaterials, the antiferromagnetic interlayer exchange energy is purposefully reduced below the out‐of‐plane demagnetization energy, which controls magnetic domain formation. In this unusual magnetic energy regime, as demonstrated via macroscopic magnetometry and microscopic Lorentz transmission electron microscopy, it becomes possible to stabilize nanometer‐scale stripe and bubble textures consisting of ferromagnetic out‐of‐plane domain cores separated by antiferromagnetic in‐plane Bloch‐type domain walls. This unique coexistence of mixed ferromagnetic/antiferromagnetic order on the nanometer scale opens so far unexplored perspectives in the architecture of magnetic domain landscapes as well as the design and functionality of individual magnetic textures, such as bubble domains with depth‐wise alternating chirality.

Affinity of Nicotinoids to a Model Nicotinic Acetylcholine Receptor (nAChR) Binding Pocket in the Human Brain.

The binding affinity of nicotinoids to the binding residues of the α4β2 variant of the nicotinic acetylcholine receptor (nAChR) was identified as a strong predictor of the nicotinoid's addictive character. Using ab initio calculations for model binding pockets of increasing size composed of 3, 6, and 14 amino acids (3AA, 6AA, and 14AA) that are derived from the crystal structure, the differences in binding affinity of 6 nicotinoids, namely, nicotine (NIC), nornicotine (NOR), anabasine (ANB), anatabine (ANT), myosmine (MYO), and cotinine (COT) were correlated to their previously reported doses required for increases in intracranial self-stimulation (ICSS) thresholds, a metric for their addictive function. By employing the many-body decomposition, the differences in the binding affinities of the various nicotinoids could be attributed mainly to the proton exchange energy between the pyridine and non-pyridine rings of the nicotinoids and the interactions between them and a handful of proximal amino acids, namely Trp156, Trpβ57, Tyr100, and Tyr204. Interactions between the guest nicotinoid and the amino acids of the binding pocket were found to be mainly classical in nature, except for those between the nicotinoid and Trp156. The larger pockets were found to model binding structures more accurately and predicted the addictive character of all nicotinoids, while smaller models, which are more computationally feasible, would only predict the addictive character of nicotinoids that are similar to nicotine. The present study identifies the binding affinity of the guest nicotinoid to the host binding pocket as a strong descriptor of the nicotinoid's addiction potential, and as such it can be employed as a fast-screening technique for the potential addiction of nicotine analogs.

Magnon Orbital Nernst Effect in Honeycomb Antiferromagnets without Spin-Orbit Coupling.

Recently, topological responses of magnons have emerged as a central theme in magnetism and spintronics. However, resulting Hall responses are typically weak and infrequent, since, according to present understanding, they arise from effective spin-orbit couplings, which are weaker compared to the exchange energy. Here, by investigating transport properties of magnon orbital moments, we predict that the magnon orbital Nernst effect is an intrinsic characteristic of the honeycomb antiferromagnet and therefore, it manifests even in the absence of spin-orbit coupling. For the electric detection, we propose an experimental scheme based on the magnetoelectric effect. Our results break the conventional wisdom that the Hall transport of magnons requires spin-orbit coupling by predicting the magnon orbital Nernst effect in a system without it, which leads us to envision that our work initiates the intensive search for various magnon Hall effects in generic magnetic systems with no reliance on spin-orbit coupling.

First principle investigation of half metallic ferromagnetism and thermoelectric behavior of MgSm2(S/Se)4 spinels for spintronic and energy harvesting applications

Density functional theory investigates the spin-dependent structural, electronic, magnetic, and thermoelectric properties of MgSm2 × 4 (X = S, Se). The optimization uses PBEsol-GGA to compute the lattice constant, bulk modulus, and energies. The Heisenberg model has been applied to calculate the Curie temperature which shows ferromagnetism above room temperature. The negative values of formation energy confirm their thermodynamic stability. The half-metallic ferromagnetism (HMF) is observed from the metallic character in the spin-up channel and insulating behaviour in the spin-down channel. The density of states plots indicates that 4f-states of Sm, 3s states of Mg and 3p/4p states of S/Se play a crucial role in forming band edges. The computation of exchange energies and exchange magnetic constants has assisted in determining these spinels' ferromagnetic and 100 % spin polarized nature. The magnetic moments (MM) arise from the p-f hybridization of Sm and X atoms. The robust half-metallicity and high Curie temperature make the studied materials suitable for spintronic applications. In addition, calculating temperature dependent thermoelectric parameters reveals an extra degree of applications of these materials for thermoelectric devices.

Effect of exchange rate uncertainty, energy prices and sectoral spending on agriculture value added, household consumption, and domestic investment

The agricultural value chain is underpinned by the interdependence of agricultural value added, household consumption and domestic investment. Understanding the complex interactions between these microeconomic outcomes and the uncertainties in the macroeconomic variables of exchange rates, energy prices and sectoral spending remains under-researched. Therefore, this study examines the impact of exchange rate, energy prices and sectoral spending on agricultural value added, household consumption and domestic investment in Nigeria from 1981 to 2020. Using Kernel regularized least squares (KRLS), the results show that the average pointwise marginal effects of exchange rate and agricultural spending are positive, while the average pointwise marginal effect of energy price is significantly negative for the agricultural value-added model. The results also show that the exchange rate, energy prices and agricultural expenditure all have a positive effect on household consumption. Regarding domestic investment, the effect of the exchange rate is positive and statistically insignificant, while the effects of energy prices and agricultural expenditure are negative and statistically significant. The study recommends the need to strengthen the social safety nets currently in place in Nigeria to support households that are vulnerable to exchange rate fluctuations. In addition, incentives should be given to households and farmers to help use renewable energy sources such as solar or wind power for agricultural activities. Also, investment in value chains and agribusiness initiatives should be encouraged rather than just in crop production.

Control of spin on ferromagnetism and thermoelectric properties of Sr(V/Cr)2S4; emergent spintronic aspirant

Strontium-based spinel chalcogenides are promising materials for energy harvesting and spintronics. Therefore, the electronic, ferromagnetic, and thermoelectric properties of SrZ2S4 (Z = V, Cr) spinels are thoroughly investigated. The formation energy and energy released during optimization demonstrate the stability of the cubic phase in a ferromagnetic state. The spin polarisation and the Curie temperature have been calculated using the density of states (DOSs) and the Heisenberg model. To explore ferromagnetism, exchange energies, the double exchange mechanism, exchange constants, and the hybridization process have all been used. The decrease in the magnetic moment for V/Cr and its shift to nonmagnetic (Sr, S) sites show that ferromagnetism is caused by electron exchange rather than V/Cr atom clustering. In the end, electrical and thermal conductivities, Seeback coefficient (S), and power factor have been used to explain the thermoelectric analysis for energy applications. Ultralow thermal conductivity values lessen the impact of heat on electron spin, extending the device’s useful life. All of these aspects, when taken together, provide a comprehensive picture of the role electron exchange plays in ferromagnetism and its application in energy devices.

MgAl2O4 capping effects on the magnetic properties of TbFeCo films

We investigate MgAl2O4 (MAO) capping effects on the magnetic properties of TbFeCo films. Compared with TbFeCo films, a shift of compensation point to lower temperatures together with significantly reduced saturation magnetization is found in the case of MAO capping. An antiferromagnetic exchange coupling is observed in TbFeCo/MAO structures. This can be well explained by a double layer model with opposite phases. An exchange energy density of ∼ 0.5 erg/cm2 is obtained, which is comparable but lower than that of TbFeCo bilayers with opposite phases. Our findings may be useful for developing ultrathin TbFeCo/MAO heterostructure-based spintronic devices.

Energy prices and exchange rates in the Eurasian Economic Union: evidence from Fourier Toda-Yamamoto approach

ABSTRACT Even though there is a growing literature on the co-movement between energy and currency markets, this issue is still unclear for the Eurasian Economic Union (EEU) countries. Based on this gap in the literature, the purpose of this study is to analyse the dynamic relationships between energy prices (crude oil and natural gas) and exchange rates for the EEU countries (Armenia, Belarus, Kazakhstan, Kyrgyzstan, and Russia) for the 2015–2022 period by means of cointegration and causality approaches without and with structural shifts. While the cointegration test without structural change does not find uniform steady-state equilibrium, considering structural change in the cointegration model reveals the existence of the long-run relationship between exchange rates and energy prices. The causality analysis uncovers predictive information between energy and currency markets in the EEU countries driven by the oil market; and accounting for smooth structural breaks in causality analysis based on the Fourier Toda-Yamamoto approach reinforces these findings. The empirical findings hence imply a strong co-movement between energy and currency markets in the EEU countries shaped by the oil market.

Novel mechanism of Fe4+/Ni3+ synergistic effect via exchange energy gain for boosting water oxidation

Novel mechanism of Fe4+/Ni3+ synergistic effect via exchange energy gain for boosting water oxidation

Spurious Oscillations Caused by Density Functional Approximations: Who is to Blame? Exchange or Correlation?

We analyze the varying susceptibilities of different density functional approximations (DFAs) to present spurious oscillations on the profiles of several vibrational properties. Among other problems, these spurious oscillations cause significant errors in harmonic and anharmonic IR and Raman frequencies and intensities. This work hinges on a judicious strategy to dissect the exchange and correlation components of DFAs and pinpoint the origins of these oscillations. We identify spurious oscillations in derivatives of all energy components with respect to nuclear displacements, including those energy terms that do not involve numerical integrations. These indirect spurious oscillations are attributed to suboptimal electron densities resulting from a self-consistent field procedure using a DFA that exhibits direct spurious oscillations. Direct oscillations stem from inaccurate numerical integration of the exchange and correlation energy density functionals. A thorough analysis of direct spurious oscillations reveals that only a handful of exchange and correlation components are insensitive to spurious oscillations, giving rise to three families of functionals, BH&H, LSDA, and BLYP. Among the functionals in these families, we encounter four widespread DFAs: BLYP, B3LYP, LC-BLYP, and CAM-B3LYP. Certain DFAs like PBE appear less sensitive to spurious oscillations due to compensatory cancellations between their energy components. Additionally, we found non-negligible but small oscillations in PBE and TPSS, which could be safely employed provided a sufficiently large integration grid is used in the calculations. These findings hint at the key components of current approximations to be improved and emphasize the necessity to develop accurate DFAs suitable for studying molecular spectroscopies.