Highlights
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A comprehensive theoretical study on the low-energy electronic states of superoxide anion (${\text{O}}_{2}^{{ - }}$) is carried out, focusing on the influence of spin-orbit coupling (SOC) on these states. Utilizing the complete active space self-consistent field (CASSCF) method combined with the multireference configuration interaction method with Davidson correction (MRCI+Q) and employing the aug-cc-pV5Z-dk basis set that includes Douglas-Kroll relativistic corrections, the electron correlation and relativistic effects are accurately considered in this work. This work concentrates on the first and second dissociation limits of ${\text{O}}_{2}^{{ - }}$, calculating the potential energy curves (PECs) and spectroscopic constants of 42 Λ-S states. After introducing SOC, 84 Ω states are obtained through splitting, and their PECs and spectroscopic constants are calculated. Detailed data of the electronic states related to the second dissociation limit are provided. The results show excellent agreement with those in the existing literature, thus validating the reliability of the method. This work confirms through calculations with different basis sets that the double-well structure of the ${{\text{a}}^{4}}{{\Sigma }}_{\text{u}}^{{ - }}$ state originates from avoiding crossing with the ${{2}^{4}}{{\Sigma }}_{\text{u}}^{{ - }}$ state, and finds that the size of the basis set can significantly affect the depth of its potential well. After considering SOC, the total energy of the system decreases, especially for the states with high orbital angular momentum (such as the ${{1}^{2}}{{\Phi }}_{\text{u}}$ and ${{1}^{4}}{{{\Delta }}_{\text{g}}}$ states), leading to energy level splitting and energy reduction, while other spectroscopic constants remain essentially unchanged. These findings provide valuable theoretical insights into the electronic structure and spectroscopic properties of ${\text{O}}_{2}^{{ - }}$, present important reference data for future research in fields such as atmospheric chemistry, plasma physics, and molecular spectroscopy. The datasets provided in this work are available from https://doi.org/10.57760/sciencedb.j00213.00076 .
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EDITOR'S SUGGESTION
2025, 74 (2): 025201.
doi: 10.7498/aps.74.20241330
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The free energy contained in electron drift, electron collision, and plasma density gradient, temperature, magnetic field gradient can trigger off the instabilities with different frequencies and wavelengths in hall thrusters. The instabilities will destroy the stable discharge of plasma, affecting the matching degree between the thruster and the power processing unit, and reducing the performance of the thruster. Based on this, the instabilities triggered off by electron collision, plasma density gradient, and magnetic field gradient in the hall thruster are studied by using dispersion relation derived from the fluid model. The results are shown below. 1) When in the model includes the effects of electron inertia, collision between electrons and neutral atoms, and electron drift, instability can be excited at any axial position from the near anode region to the plume region of the thruster. With the increase of azimuthal wavenumber ${k_y} = 2\pi /\lambda $, the lower-hybrid mode excited by electron collision transitions into the ion sound mode, where ${k_y} = 2{\text{π }}/\lambda $, $\lambda $being the wave length. The real frequency ${\omega _{\text{r}}}$ corresponding to the maximum growth rate ${\gamma _{\max }}$ slightly decreases with collision frequency increasing for ${k_y} = 10{\text{ }}{{\text{ m}}^{ - 1}}$. However, the maximum real frequency and real frequency ${\omega _{\text{r}}}$ corresponding to the maximum growth rate ${k_y} = 300{{\text{ m}}^{ - 1}}$ will not change with collision frequency for ${k_y} = 300{\text{ }}{{\text{ m}}^{ - 1}}$. Independent of the value of ${k_y}$, the growth rate of mode triggered off by electron collision increases with collision frequency increasing. 2) The plasma density gradient effect plays a dominant role in triggering off instabilities when the electron inertia, electron-neutral collisions and plasma density gradient are simultaneously included in the model. The dynamic behavior of the model does not change with the increase of ${k_y}$, but the eigenvalue of the model increases with the ${k_y}$ increasing. Since the sign of anti-drift frequency induced by the plasma density gradient is changed, the mode eigenvalues have the opposite change trend on both sides of point ${\kappa _{\text{N}}}$. When the sign of ${\omega _r}$ and ${\omega _r}$ are opposite, the density gradient effect has a stabilization effect on instability excitation (${\kappa _{\text{N}}} > 0$). When the sign of ${\omega _{\text{s}}}$ and ${\omega _{\text{r}}}$ are the same, the density gradient effect enhances the excitation of instability (${\kappa _{\text{N}}} < 0$). 3) If the plasma density gradient, magnetic field gradient, electron inertia and electron-neutral collisions are included in the dispersion, the mode eigenvalue relies on the electron drift frequency, and the diamagnetic drift frequency induced by the density gradient and magnetic field gradient. When the density gradient effect and the magnetic field gradient effect are considered, there is a stable window in the discharge channel. However, if the electron inertia and electron-neutral collisions are also included, the stable window will disappear.
EDITOR'S SUGGESTION
2025, 74 (2): 021401.
doi: 10.7498/aps.74.20241529
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Fast neutron multiplicity measurement technology is an important non-destructive testing technology in the field of arms control verification. In the technique, the liquid scintillation detector is used to detect the fission neutron and combined with the time correlation analysis method to extract multiplicity counting rates from the pulse signals. This technique is commonly used to measure the mass of nuclear materials, however, it is based on the point model that assumes that the neutron multiplication coefficient keeps constant in the whole spatial volume, which will lead to overestimation of the multiplication coefficient and result in system deviation. To correct the deviation and improve the measurement accuracy, the fast neutron multiplicity simulation measurements are carried out on spherical and cylindrical samples in this work. The relationship among the position of neutron generation, absorption and net growth in the space volume of the material is obtained. According to the definition of the leakage multiplication coefficient, the leakage multiplication coefficients at different positions in the space volume of the material are calculated. On this basis, a method based on spatial multiplication coefficient correction is proposed according to the functional relationship between neutron multiplicity factorial moments and the unknown parameters. In this method, the n-order multiplication coefficient is modified by introducing a weight factor $ {g_n} $, and the fast neutron multiplicity weighted point model equation is derived. To verify the accuracy of this method, a set of fast neutron multiplicity detection model is built by Geant4, and the fast neutron multiplicity simulation measurement is carried out on the spherical and cylindrical samples. The results show that the solution accuracy of the weighted point model equation is higher than that of the standard point model equation, and the measurement deviation is reduced to less than 6 %. This work provides an optimization method for solving plutonium samples with several kilograms in mass, and promotes the development of the fast neutron multiplicity measurement technology.
EDITOR'S SUGGESTION
2025, 74 (2): 024101.
doi: 10.7498/aps.74.20241196
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The transmission of 2-keV electrons through a polyethylene terephthalate (PET) nanocapillary with a diameter of 800 nm and a length of 10 μm is studied. The transmitted electrons are detected using microchannel plate (MCP) with a phosphor screen. It is found that the transmission rate for the transmitted electrons with the incident energy can reach up to 10 % for an aligned capillary in the beam direction, but drops to less than 1% when the tilt angle exceeds the geometrical allowable angle. The transmitted electrons with the incident energy do not move with change of tilt angle, so the incident electrons are not guided in the insulating capillary, which is different from the scenario of positive ions. In the final stage of the transmission, the angular distribution of the transmitted electrons within the geometrical allowable angle splits into two peaks along the observation angle perpendicular to the tilt angle. The time evolution of the transmitted full angular distribution shows that when the beam turns on, the transmission profile forms a single peak. As the incident charge and time accumulate, the transmission profile starts to stretch in the plane perpendicular to the tilt angle and gradually splits into two peaks. When the tilt angle of the nanocapillary exceeds the geometrical allowable angle, this splitting tends to disappear. Simulation of the charge deposition in the capillary directly exposed to the beam indicates the formation of positive charge patches, which are not conducive to guidance, as seen in the case of positive ions. According to the simulation results, we can explain our data. Then, the possible reasons for the splitting the transmission angular profiles are discussed.
EDITOR'S SUGGESTION
2025, 74 (2): 020201.
doi: 10.7498/aps.74.20241275
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Lithium-ion batteries (LIBs) are widely used in portable electronic devices, electric vehicles, and other fields. With the rapid development of its application fields, there is an urgent need to further improve its energy density and safety. In the charging/discharging process of the LIBs, the diffusion of Li will cause local volumetric change in the electrode material. The degradation and damage of the electrode material structure caused by diffusion-induced deformation is a major obstacle to the development of LIBs. Generally speaking, the electrode materials in LIBs are always subject to specific external constraints, including both inevitable passive structural constraints within the battery and external active constraints that may be imposed by emerging technology application scenarios, which can also affect the mechanical properties of the electrode materials. Therefore, a more in-depth understanding of the diffusion-induced stress and Li concentration changes in the electrode material is an engineering requirement for developing new material design paradigms to improve the overall performance of LIBs. In this work, a two-way diffusion-stress coupling model is used to discuss the effects of the four different levels of idealized deformation constraints on the Li concentration and stress in the bilayer plate electrode in the charging process through the numerical solution. From a mechanical perspective, the bilayer plate electrode structure has two degrees of freedom: lateral expansion and bending deformation. Weakened constraint conditions can partially or completely activate these stress release mechanisms, thereby reducing the overall stress level of the electrode structure and improving its mechanical stability. However, from an electrochemical perspective, the stress gradient generated by the forward bending deformation of the electrode structure can hinder the Li intercalation process. Enhanced constraints can partially or completely suppress the forward bending of the electrode, making the Li concentration in the active layer more uniform and thus improving the capacity utilization efficiency of the active layer. These results not only provide theoretical references for further understanding the chemical-mechanical response of the bilayer electrodes under more realistic or extreme service conditions, but also indicate from a design perspective that compromised external constraints are beneficial for balancing the structural durability and electrochemical performance of electrodes.
EDITOR'S SUGGESTION
2025, 74 (2): 028101.
doi: 10.7498/aps.74.20241294
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Although phosphorescent organic light-emitting devices (OLEDs) can have an internal quantum efficiency (IQE) of 100%, the IQE usually decays at high current densities due to triplet-triplet annihilation. Phosphor-sensitized fluorescence can realize the energy transfer between phosphorescent emitter and fluorescent emitter, and can be used to suppress the efficiency fluctuations and adjust the color of the device. With this in mind, white light emission including different colors of phosphorescent emitter and fluorescent emitter can be expected. Herein, phosphor-sensitized fluorescent white OLEDs are fabricated by combining ultra-thin layer insertion and doping, in which laser dyes DCM (4-(Dicyanomethylene)-2-methyl-6-(4-dimethyl-aminostyryl)-4H-pyran), iridium complexes Ir(ppy)3 (tris(2-phenylpyridine)iridium), and biphenyl ethylene derivatives BCzVB (1,4-bis[2- (3-N-ethylcarbazoryl)vinyl]benzene) are used as red, green and blue emitters, respectively. By adjusting the doping concentration of Ir(ppy)3 phosphorescent green emitter in CBP (4,4’-N,N’-dicarbazole-biphyenyl) host, with ultra-thin layers of BCzVB fluorescent blue emitter on both sides of CBP:Ir(ppy)3 doping system and with ultra-thin layer of DCM fluorescent red emitter inserting in CBP:Ir(ppy)3 layer, the three colors can be balanced. White emissions are obtained in the device, the highest external quantum efficiency is 2.5% (current efficiency of 5.1 cd/A), the maximum brightness is 12400 cd/m2, and Commission Internationale de l'Eclairage (CIE) co-ordinates can reach the ideal white light equilibrium point (0.33, 0.33) at a current density of 1 mA/cm2. The acquisition of white light is attributed to the appropriate doping ratio of Ir(ppy)3 and the position of DCM, which effectively balances the emission ratio of three primary colors: red, green, and blue. The results indicate that the partially energy transfer of triplet excitons to singlet excitons by phosphor-sensitized fluorescence scheme can be used to realize high-efficiency white organic electroluminescent devices, thereby reducing energy consumption and providing more room for promoting OLED applications.
EDITOR'S SUGGESTION
2025, 74 (2): 027501.
doi: 10.7498/aps.74.20241340
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Rare-earth elements share similar ground-state electronic properties, and their unique lanthanide contraction effect can lower the mixing enthalpy of rare-earth elements in high-entropy materials, which is of great significance for fabricating low-cost and high-performance high-entropy rare-earth intermetallic compounds. In this work, the magnetization reversal mechanisms of rapidly quenched ribbons such as Nd11.76Fe82.36B5.88 (NdFeB) and the relevant high-entropy rare-earth permanent magnet alloy compounds (La0.2Pr0.2Nd0.2Gd0.2Dy0.2)11.76Fe82.36B5.88 and (La0.2Pr0.2Nd0.2Gd0.2Tb0.2)11.76Fe82.36B5.88 are studied by analyzing the magnetization and demagnetization curves, supplemented by Henkel curves and magnetic viscosity coefficient S. Compared with the pure NdFeB sample, the high-entropy rare-earth permanent magnet has the inter-grain exchange coupling significantly enhanced and the magnetic dipole interaction weakened, indicating that the element diffusion mechanism in heavy rare-earth containing high-entropy material homogenizes the sample, and significantly increases the coercivity. The mechanism of the coercivity is the nucleation of magnetization reversal domains in the grains of the hard magnetic phase. The magnetization mechanism is dominated by pinning at low magnetic fields and by nucleation at high magnetic fields, which is different from the magnetization mechanism of pure NdFeB and has some similarities with the self-pinning mechanism. The magnetic viscosity coefficient of (La0.2Pr0.2Nd0.2Gd0.2Dy0.2)11.76Fe82.36B5.88 is larger than that of pure NdFeB. Due to the asynchrony of hard magnetic phase reversal and intergranular magnetic coupling in (La0.2Pr0.2Nd0.2Gd0.2Tb0.2)11.76Fe82.36B5.88, the magnetic viscosity coefficient is small but the anisotropy field is large. This indicates that high-entropy sample reduces the magnetocrystalline anisotropy field barrier but increases the magnetocrystalline coupling length. This suggests that the magnetization reversal of high-entropy rare-earth permanent magnet material is significantly different from that of conventional rare earth permanent magnet material and it is worthy of further in-depth research.
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