The European Physical Journal B最新文献

Water molecules with their hydrogen bonding capability, exhibit exceptional properties in the bulk as well as in cluster form. In the present work, we study the size-dependent trends in the structure, energetics, bonding, ionisation potential, fragmentation pattern, and optical properties of water clusters in the size range of n = 2–20, and an interplay between them. We have extensively searched for the lowest energy structures of the water clusters using the artificial bee colony algorithm, optimised them first with the classical force field TIP4P and then relaxed at least 10 lowest energy structures using density functional theory. We have found new lowest energy structures for all the sizes as against the ones reported earlier. The structures and stability of water clusters are primarily dictated by the H-bond network. However, we found the weak van der Waals interactions also play a crucial role in stabilising the clusters giving them unique characteristics. Some of the clusters such as those with (n=4, 8, 10, 12) and 15 molecules were structurally symmetric, yet a close analysis of various properties reveals that the clusters with (n=4, 8, 12, 14) and 19 molecules are more stable than others. Spherical or nearly spherical clusters were found to be the most stable, corroborated by the shape deformation parameters and the fragmentation pattern, which indicated a higher likelihood of forming fragments of sizes (n=4, 8, 12, 14), and 16. A blueshift of the H-O-H vibrational modes and a redshift of the O–H stretching modes is seen for most clusters. Such characteristics in the vibrational spectra is associated with an increase in the H-bond strength which is seen to increase with size of the cluster. Large optical band gaps for (n=4, 8, 12) and 16 along with blueshifts in optical spectra implies these clusters to be chemically more stable than others.

This study investigates the structural, optical, and electrochemical properties of MgNiP₂O₇, a promising material for energy storage and catalysis applications. The compound was synthesized using a sol–gel method and characterized through X-ray diffraction, Fourier-transform infrared spectroscopy, and UV–visible spectroscopy. X-ray analysis confirmed a monoclinic crystal structure with space group P21/c. Optical studies revealed two distinct band gap energies at 1.6 eV and 2.66 eV, indicating potential for optoelectronic applications. Electrochemical characterization, including cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry, enhanced electrocatalytic activity, particularly for the oxygen reduction reaction. The material exhibited high current density and stable performance over time, suggesting its suitability for energy storage systems such as batteries and fuel cells. These findings highlight the multifunctional nature of MgNiP₂O₇ and its potential significance in developing sustainable energy technologies and environmental applications.

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Single-crystal N-acetyl-l-alanine (NALA), a semi-organic crystal, has been synthesized by slow evaporation growth technique in aqueous medium. An experimental study proves that it has the space group of P2₁2₁2 and orthorhombic crystal system. The unit-cell parameters of NALA crystal were identified using single-crystal XRD analysis. UV–vis analysis has been used to find out the cut-off wavelength of the crystal. The calculated Urbach energy and the related optical constant values support the non-linear optics (NLO) nature of NALA crystal. SEM and EDAX experiments were carried out to find the surface and elemental characteristics of the NALA crystal. Vickers micro-hardness studies have been utilized to probe the mechanical stability of the crystal. Kurtz–Perry Simple Harmonic Generation (SHG) study has suggested 1.4 times greater NLO efficiency of NALA crystal than that of standard KDP. Thermal stability of the crystal is demonstrated by TGA and DTA analysis. Glass transition (T_g) temperature is achieved through DSC analysis. Coats–Redfern method has been used to explain the thermodynamic parameters. The theoretical calculation done by density functional theory (DFT) and the computed values of polarizability calculations of NALA are compared and justifiable with the standard values. Polarizability and first-order hyperpolarizability (both static and dynamic) are calculated to see the potential application in non-linear optics and it is observed that the values are found to be 2.7 times greater than those of prototype at the same theoretical functional. The frontier study of HOMO–LUMO is used to interpret the global chemical molecular descriptors and indicate the applicability of the NALA crystal toward optical device fabrication.

Graphical Abstract

Hydrogen bonding graphical extract

The study investigates the photoacoustic pressure effects on microtemperature distributions within a nanostructured (nonlocal) elastic semiconductor medium, where thermal conductivity is considered variable. Photoacoustic phenomena, which involve the generation of acoustic (elastic) waves due to the absorption of modulated light, play a pivotal role in heat transfer dynamics at the nanoscale. The interaction between photoacoustic pressure, plasma waves, and thermal waves influences localized temperature variations in semiconductor nanostructures. The variable thermal conductivity, which accounts for temperature dependence and nanoscale effects, adds complexity to the heat diffusion process. Using mathematical modeling and numerical simulations, the photoacoustic pressure-driven thermal response is analyzed in one dimension (1D) under different excitation frequencies and thermal conductivity profiles. Results show that the variable thermal conductivity significantly affects the propagation of thermal waves, acoustic pressure, elastic, mechanical, microtemperature, and carrier density diffusion, leading to enhanced heat confinement or dispersion depending on material properties and operating conditions. The findings have implications for the design of semiconductor devices where thermal management is critical, such as in photodetectors, microelectronic systems, and optoelectronic devices. This research advances the understanding of nanoscale heat transfer mechanisms in semiconductors under photoacoustic excitation and provides insight into optimizing thermal performance in nanostructured materials.

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Delocalized nonlinear vibrational modes (DNVMs) in crystals are precise solutions to the equations governing atomic motion that are determined solely by the symmetry of the lattice. This study investigates the influence of two-dimensional discrete breathers (DBs) excited using four one-component DNVMs on the macroscopic properties of three-dimensional fcc single crystals of Al, Cu, and Ni. All results were obtained using molecular dynamics simulations. Key findings include the observation that the lifetime of two-dimensional DBs is significantly influenced by both the symmetry of the DNVM and the initial oscillation amplitude. The two-dimensional DBs exhibit hard-type nonlinearity, characterized by an increase in oscillation frequency with increasing initial amplitude. The excitation of the DBs leads to a reduction in the crystal's heat capacity, which becomes more pronounced with increasing amplitude. The presence of two-dimensional DBs induces thermal expansion within the crystal, suggesting an impact on the mechanical properties of the material. This research provides new insights into the role of DBs, in influencing the macroscopic properties of fcc metals.

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The first-principles calculation method is performed to explore the monolayer 2H-MoS₂:Fe semiconductors with intrinsic ferromagnetism and strong ferromagnetic coupling by strain-modulation. In this study, we demonstrate that the biaxial strain can effectively regulate the distribution of local magnetic moment, magnetic coupling ground state types and strength. The studied results indicate that one Fe_Mo dopant will bring 2 (mu_{{text{B}}}) local magnetic moment, which is not affected by strains in range of − 6~6%. However, electronic configuration, occupation and magnetic moment distribution are closely related to strains. Moreover, smaller compressive strain can effectively strengthen ferromagnetic interactions between two Fe_Mo substitutions, and the most energy gains of ferromagnetic coupling reach to 153.9 meV under − 2% strain. However, the ferromagnetic ground state translates into antiferromagnetic one as strain in the range of − 6~ − 2.5%. The changes in magnetic moment and magnetic interaction originate from the competition between crystal-filed splitting and spin splitting under different strains. The theoretical results presented here predict that modulating the biaxial strain could be a very significant avenue to obtain intrinsic ferromagnetic 2H-MoS₂:Fe semiconductors.

Graphical abstract

The effect of strain on the electronic structures and magnetic properties of Fe doped monolayer 2H-MoS₂ were studied by first-principles calculations. We found that electronic configuration, occupancy and magnetic moment distribution are closely related to strains. Smaller compressive strain can effectively strengthen FM interactions between two Fe_Mo substitutions, and the most energy gains of FM coupling up to 153.9 meV under − 2% strain. However, the FM ground state translate into AFM one as strain in the range of − 6~− 2.5%. Our theoretical predictions highlight the important contribution of strain to electronic structures and magnetic properties, and present a valid avenue for the future design of high T_C material in monolayer MoS₂: Fe system.

Models for resident infectious diseases, like the SIRS model, may settle into an endemic state with constant numbers of susceptible (S), infected (I) and recovered (R) individuals, where recovered individuals attain a temporary immunity to reinfection. For many infectious pathogens, infection dynamics may also show periodic outbreaks corresponding to a limit cycle in phase space. One way to reproduce oscillations in SIRS models is to include a non-exponential dwell-time distribution in the recovered state. Here, we study a SIRS model with a step-function-like kernel for the immunity time, mapping out the model’s full phase diagram. Using the kernel series framework, we are able to identify the onset of periodic outbreaks when successively broadening the step-width. We further investigate the shape of the outbreaks, finding that broader steps cause more sinusoidal oscillations while more uniform immunity time distributions are related to sharper outbreaks occurring after extended periods of low infection activity. Our main results concern recovery distributions characterized by a single dominant timescale. We also consider recovery distributions with two timescales, which may be observed when two or more distinct recovery processes co-exist. Surprisingly, two qualitatively different limit cycles are found to be stable in this case, with only one of the two limit cycles emerging via a standard supercritical Hopf bifurcation.