分类： 物理学 >> 核物理学 提交时间： 2023-07-12
摘要： The in-medium feature of nuclear force which includes both nucleon-nucleon (NN) and hyperon-nucleon (\Lambda N) interactions impacts the description of single-\Lambda hypernuclei. With the alternated mass number or isospin of hypernuclei, such effects could be unveiled by analyzing systematical evolution of the bulk and single-particle properties. From a density-dependent meson-nucleon/hyperon coupling perspective, a new \Lambda N effective interaction in the covariant density functional (CDF) theory, namely DD-LZ1-\Lambda1, is obtained by fitting the experimental data of \Lambda separation energies for several single-\Lambda hypernuclei. It is then adopted to study the structure and transition properties of single-\Lambda hypernuclei in Oxygen isotopes, comparing with several selected CDF Lagrangians. Discrepancy is observed explicitly in the isospin evolution of \Lambda1p spin-orbit splitting with various effective interactions, ascribed to their divergence of the meson-hyperon coupling strengths with increasing density. In particular, the density-dependent CDFs introduce an extra contribution to enhance the isospin dependence of the splitting, which is originated from the rearrangement terms of \Lambda self-energies. In addition, the characteristics of hypernuclear radii are studied along the isotopic chain. Owing to the impurity effect of \Lambda hyperon, a size shrinkage is observed in the matter radii of hypernuclei as compared to their cores of normal nuclei, while its magnitude is elucidated further to correlate with the incompressibility of nuclear matter. Besides, there exists a sizable model-dependent trend that \Lambda hyperon radii evolve with the neutron number, which is decided partly by the in-medium NN interactions as well as the core polarization effects.
分类： 物理学 >> 核物理学 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： We performed density functional theory calculations of H, C, and O chemisorption on the UN(001) and (111) surfaces using the generalized gradient approximation (GGA) and the Hubbard U parameter and revised Perdew-Burke-Ernzerhof (RPBE) exchange-correlation functional at non-spin polarized level with the periodic slab model. Chemisorption energies vs. distance of molecules from UN(001) and UN(111) surfaces have been optimized for four symmetrical chemisorption sites, respectively. The results show that the Hollow, N-top, and Hollow adsorption sites are the most stable sites for H, C, and O atoms with chemisorption energies of 13.06, 25.50 and 27.34 kJ/mol for UN(001) surface, respectively. From the point of adsorbent (UN(001) and UN(111) surfaces in this paper), interaction of O with the chemisorbed surface is of the maximum magnitude, then C and H, which are in agreement with electronegativities of individual atoms. For the UN(001) surface, U-N bond lengths change relatively little (10%). Electronic structure calculations indicate that Bridge position is equivalent with Hollow position, and the most stable chemisorption position for H, C, and O atoms are all Bridge (or Hollow) position for the UN(111) surface. Calculated electronic density of states (DOSs) demonstrate electronic charge transfer between s, p orbitals in chemisorbed atoms and U 6d, 5f orbitals.
分类： 化学 >> 核化学 提交时间： 2023-06-06
Zhang, Hang
Ao, Yin-Yong
Wang, Yue
Zhao, Shang-Jie
Sun, Jia-Yang
Zhai, Mao-Lin
Li, Jiu-Qiang
Peng, Jing
Li, Hui-Bo
摘要： N,N,N,N-Tetraoctyl diglycolamide (TODGA) is one of the most promising extractants tailored for high-level liquid radioactive waste treatment during nuclear fuel reprocessing. The -radiolysis of TODGA (0.2 mol/L) in n-dodecane (nDD) solution with and without pre-equilibrated 3.0 mol/L HNO3 was investigated using HPLC and UPLC-QTOF-MS and compared with the -radiolysis of neat TODGA in this study. With increased absorbed doses, the concentration of TODGA decreased exponentially for the studied systems. Moreover, pre-equilibration with HNO3 (3.0 mol/L) slightly influenced the -radiolysis of TODGA in nDD. Seven radiolytic products generated from the rupture of the C C, C O, and C N bonds in TODGA were identified in the studied extraction system. The influence of -radiation on TODGA/nDD for the extraction of Eu(III) was evaluated using the first combination of extraction experiments and density functional theory (DFT) calculations, in which the complexations of Eu(III) with TODGA and its radiolytic products were systematically compared. Based on the radiolysis kinetic model of TODGA, the slope curve of the distribution ratio of Eu(III) (DEu ) and the absorbed dose, and fluorescence titration analysis, the empirical equation of the absorbed dose and DEu was obtained successfully. Below 300 kGy, the experimental DEu agreed well with the obtained empirical equation for TODGA/nDD. Conversely, at a high absorbed dose, the experimental DEu was higher than the theoretical DEu based on the empirical equation because the radiolytic products of TODGA with similar coordination structures still possessed partial complexation toward Eu(III), which was confirmed by DFT calculations. This work provides a method to predict the extraction distribution ratio of an irradiated extractant system and to understand the complex extraction process.
分类： 核科学技术 >> 辐射物理与技术 提交时间： 2024-04-12
摘要： A microscopic method for calculating nuclear level density (NLD) based on the covariant density functional theory (CDFT) is developed. The particle-hole state density is calculated by combinatorial method using the single-particle levels schemes obtained from the CDFT, and then the level densities are obtained by taking into account collective effects such as vibration and rotation. Our results are compared with those from other NLD models, including phenomenological, microstatistical and non-relativistic HFB combinatorial models. The comparison suggests that the general trends among these models are basically the same, except for some deviations from different NLD models. In addition, the NLDs of the CDFT combinatorial method with normalization are compared with experimental data, including the observed cumulative number of levels at low excitation energy and the measured NLDs. Compared with the existing experimental data, the CDFT combinatorial method can give reasonable results.
分类： 物理学 >> 核物理学 提交时间： 2024-02-26
摘要： Since the discovery of the halo nucleus 11Li in 1985, halo phenomena in exotic nuclei have always been an important frontier in nuclear physics research. The relativistic density functional theory has achieved great success in the study of halo nuclei, e.g., the self-consistent description of halo nucleus 11Li and the microscopic prediction of deformed halo nuclei. This paper introduces some recent progresses, including the investigation of halo nucleus 37Mg and the prediction of the N = 28 shell collapse and a deformed halo in the new isotope 39Na based on the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc), as well as the exploration of triaxially deformed halo nuclei by the newly developed triaxial relativistic Hartree-Bogoliubov theory in continuum (TRHBc).
分类： 物理学 >> 核物理学 提交时间： 2017-07-30
摘要： Symmetry plays a fundamental role in physics. The quasi-degeneracy between single-particle orbitals (n, l, j = l + 1/2) and (n − 1, l + 2, j = l + 3/2) indicates a hidden symmetry in atomic nuclei, the so-called pseudospin symmetry (PSS). Since the introduction of the concept of PSS in atomic nuclei, there have been comprehensive efforts to understand its origin. Both splittings of spin doublets and pseudospin doublets play critical roles in the evolution of magic numbers in exotic nuclei discovered by modern spectroscopic studies with radioactive ion beam facilities. Since the PSS was recognized as a relativistic symmetry in 1990s, many special features, including the spin symmetry (SS) for anti-nucleon, and many new concepts have been introduced. In the present Review, we focus on the recent progress on the PSS and SS in various systems and potentials, including extensions of the PSS study from stable to exotic nuclei, from non-confining to confining potentials, from local to non-local potentials, from central to tensor potentials, from bound to resonant states, from nucleon to anti-nucleon spectra, from nucleon to hyperon spectra, and from spherical to deformed nuclei. Open issues in this field are also discussed in detail, including the perturbative nature, the supersymmetric representation with similarity renormalization group, and the puzzle of intruder states.
分类： 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间： 2019-07-02
摘要： P. W. Anderson raised an important question in 2007: Is There Glue in Cuprate Superconductors? The author believes that the change of the electron clouds of ions is the glue in cuprate superconductors. The change of the electron clouds of the ions in the parent structure of the layered high-temperature superconductors CaCuO2 has been studied by the first-principles calculations. The electron clouds of Cu2+ and O2- ions change obviously under electric fields. It is also found, for the first time, the characteristic frequencies of the change of the electron clouds are 250 meV, 360 meV, and 100 meV, respectively, for the modes observed. The frequencies are low and close to that of lattice vibrations, indicating the change of the electron cloud of ions can be the electron-pairing medium in cuprate superconductors.
分类： 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间： 2019-04-24
摘要： The electron-pairing mechanism in unconventional high temperature superconductors (HTS) has not been resolved. The author proposed that the electron-pairing medium of unconventional HTS is the change of the electron clouds of transition metal ions, which is analogous to the lattice vibration in conventional superconductors. Real-time evolution of the electron clouds of transition metal ions under excitations in La2Fe2As2O2, FeSe sheet, Fe2KSe2, CaCuO2, and HgBa2Ca2Cu3O8 was calculated by the time-dependent density functional theory (TDDFT). The characteristic frequency is about 90-250 meV, which is equivalent to the lattice vibration frequencies, showing that the change of the electron clouds of the transition metal ions can be the electron-pairing medium in unconventional HTS.
分类： 化学 >> 物理化学 提交时间： 2017-11-05 合作期刊: 《结构化学》
摘要： The adsorption process and hydrogenation mechanisms of 2-methylthiophene on the Pt(111) surface have been elucidated using density functional theory (DFT). The optimal adsorption sites of reactants, intermediates, and products as well as the activation energy and reaction energy of each elementary reactions were investigated. The results turned out that the 2-methylthiophene tilt to the Pt(111) catalyst with the C1–C2 double bond at the top site was the most stable. During the hydrogenation process, the heat of reaction almost located at the negative side, so dropping the temperature is good for the occurrence of hydrogenation process. The hydrogenation steps of mechanism take place along C2→C3→C1→C4→S→C1 to generate the product of pentane-2-thiol, in which the first step with the highest energy barrier is the rate-determining step.
分类： 物理学 >> 核物理学 提交时间： 2023-07-03
摘要： Following the reports of candidate chiral doublet bands observed in cesium isotopes, the possible chiral candidates and the evolution of three-dimensional rotation in ^{120-134}{ textrm{Cs}} are investigated within the microscopic three-dimensional tilted axis cranking covariant density functional theory (3DTAC-CDFT). By investigating the evolution of the polar angle theta and azimuth angle varphi as a function of rotational frequency hbar omega, the transition from the planar rotation to the chiral rotation has been found in ^{121-133}{ textrm{Cs}}. The corresponding critical rotational frequency omega_{ textrm{crit}} of the appearance of chiral aplanar rotation decreases as neutron number increases, which can be attributed to the neutrons in (gd) and (sd) shells having smaller angular momentum components along both the short and long axes, and larger components along medium axis, respectively. In comparison, only planar rotation has been obtained in ^{120,134}{ textrm{Cs}}. With these interpretations, the obtained I sim hbar omega and energy spectra as well as B(M1)/B(E2) values show reasonable agreement with the available experimental data. In addition, the evolution of quadrupole deformation beta and triaxial deformation gamma are also discussed.
分类： 化学 >> 物理化学 提交时间： 2017-11-05 合作期刊: 《结构化学》
摘要： The structural, electronic, and magnetic properties of ConO (n = 2～10) clusters have been systematically investigated within the framework of the generalized gradient approximation density functional theory. The results indicate that the O atom occupies the surface-capped position on ConO (n = 2～10) clusters. The stabilities of the host clusters are improved by adding one O atom. Maximum peaks of the second-order difference energy of the ground-state ConO clusters are found at n = 3, 6 and 8, indicating higher stability than their neighboring clusters. Compared with corresponding pure Con clusters, the O-doped cobalt clusters have larger gaps between the HOMO and LUMO energy levels, indicating their higher chemical stabilities. In addition, the doping of O atom exhibits different influence on the magnetism of the clusters. This is also further investigated by the local magnetic moment, deformation charge density and partial local density of states analysis.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2024-09-10
摘要： We report a comprehensive study on the low-lying parity-doublet states of ^{224}Rn with the mixing of both quadrupole and octupole-shaped configurations in a multireference covariant density functional theory, where the symmetries broken in the configurations are restored with projection techniques. The low-lying energy spectrum is reasonably reproduced. The electric octupole transition strength in ^{224}Rn is found to be B(E3; 3^-_1 \rightarrow0^+_1)=43 W.u., comparable to that in ^{224}Ra, whose data are 42(3) W.u. Our results indicate that ^{224}Rn shares a similar low-energy structure with ^{224}Ra, despite the first 3^- state of the former nucleus being higher in energy than that of the latter. This study suggests ^{225}Rn to be another candidate to search for a permanent electric dipole moment.
分类： 核科学技术 >> 辐射物理与技术 提交时间： 2024-07-04
摘要： The octupole deformation and collectivity in octupole double-magic nucleus144Ba are investigated using theCranking covariant density functional theory in a three-dimensional lattice space. The reducedB(E3)transi#2;tion probability is implemented for the first time in semiclassical approximation based on the microscopicallycalculated electric octupole moments. The available data, including theI–ωrelation and electric transitionalprobabilitiesB(E2)andB(E3)are well reproduced. Furthermore, it is shown that the ground state of144Baexhibits axial octupole and quadrupole deformations that persist up to high spins (I≈24ℏ).
分类： 物理学 >> 核物理学 提交时间： 2023-07-17
摘要： Based on the covariant density functional theory, by employing the core--quasiparticle coupling (CQC) model, the nuclear level density of odd-A nuclei at the saddle point is achieved. The total level density is calculated via convolution of the intrinsic level density and the collective level density. The intrinsic level densities are obtained in the finite-temperature covariant density functional theory, which takes into account the nuclear deformation and pairing self-consistently. For saddle points on the free energy surface in the (\beta_2, \gamma) plane, the entropy and the associated intrinsic level density are compared with those of the global minima. By introducing a quasiparticle to the two neighboring even--even core nuclei, whose properties are determined by the five-dimensional collective Hamiltonian model, the collective levels of the odd-A nuclei are obtained via the CQC model. The total level densities of the ^{234-240}U agree well with the available experimental data and Hilaire's result. Furthermore, the ratio of the total level densities at the saddle points to those at the global minima and the ratio of the total level densities to the intrinsic level densities are discussed separately.
分类： 物理学 >> 凝聚态:结构、力学和热性能 提交时间： 2020-08-23
摘要： 实验测量表明体心立方固溶体 约在 2.0 at.% Mn发生相变，但这一相变的机制，相变前后铁锰体系的物理性质变化至今仍不清楚。本文通过密度泛函计算，揭示了这一相变是一种同构相变，并阐明了相变机制和相变前后物理性质的变化。
分类： 物理学 >> 核物理学 提交时间： 2024-02-21
摘要： By the Skyrme density functional theory (DFT), potential energy surfaces (PES) of ^{240}Pu with constraints on the axial quadrupole and octupole deformations(q_{20} and q_{30}) are calculated.The volume-like, and the surface-like pairing forces, and the mixing between these two forces are used, within the Hartree-Fock-Bogoliubov (HFB) approximation. The variations of the least-energy fission path, fission barrier, paring energy, total kinetic energy, scission line, and mass distribution of fission fragments by the different forms of paring force are analyzed and discussed. The fission dynamics is studied based on the time-dependent generator coordinate method (TDGCM) plus Gaussian overlap approximation (GOA). The results show a sensitivity of the mass and charge distributions of fission fragments to the form of the pairing force. Based on the investigation of the neutron-induced fission of ^{239}Pu, among the volume, mixed, and surface pairing forces, the mixed-type of pairing force can give a good reproduction of experimental data.
分类： 核科学技术 >> 核材料与工艺技术 提交时间： 2023-08-14
摘要： Alloys of uranium and molybdenum are considered as the future of nuclear fuel and defense materials. However, surface corrosion is a fundamental problem in practical applications and storage. In this study, the static and dynamic evolution of carbon monoxide (CO) adsorption and dissociation on -U (1 0 0) surface with different Mo doping levels was investigated based on density functional theory and ab initio molecular dynamics. During the static calculation phase, parameters, such as adsorption energy, configuration, and Bader charge, were evaluated at all adsorption sites. Furthermore, the time-dependent behavior of CO molecule adsorption were investigated at the most favorable sites. The minimum energy paths for CO molecular dissociation and atom migration were investigated using the transition state search method. The results demonstrated that the CO on the uranium surface mainly manifests as chemical adsorption before dissociation of the CO molecule. The CO molecule exhibited a tendency to rotate and tilt upright adsorption. However, it is difficult for CO adsorption on the surface in one of the configurations with CO molecule in vertical direction but oxygen (O) is closer to the surface. Bader charge illustrates that the charge transfers from slab atoms to the 2* antibonding orbital of CO molecule and particularly occurs in carbon (C) atoms. The time is less than 100 fs for the adsorptions that forms embryos with tilt upright in dynamics evolution. The density of states elucidates that the overlapping hybridization of C and O 2p orbitals is mainly formed via the d orbitals of uranium and molybdenum (Mo) atoms in the dissociation and re-adsorption of CO molecule. In conclusion, Mo-doping of the surface can decelerate the adsorption and dissociation of CO molecules. A Mo-doped surface, created through ion injection, enhanced the resistance to uranium-induced surface corrosion.
分类： 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间： 2019-06-13
摘要： It is proposed that the electron-pairing medium of the iron-based superconductors may be the orbital fluctuation of the transition metal ions. But the characteristic frequency of the orbital fluctuation has not been given. For the first time, the author has calculated the real-time evolution of the electron clouds of transition metal ions in BaFe2As2 under excitations by the time-dependent density functional theory (TDDFT). There are different modes of fluctuations. The characteristic frequencies are 150 meV, 160 meV, 250 meV, and 200 meV, respectively, for the modes the author observed. The results are unexpected, because the general view is that the change of the electron density is very quick, and the frequency is much higher than the lattice vibration. The frequencies the author obtained are close to that of the lattice vibration in conventional superconductors at normal and high pressures, indicating the orbital (or electron cloud) fluctuation can by the electron pairing medium. Based on the calculation results, the author proposed a new electron pairing mechanism.
分类： 材料科学 >> 金属与冶金 提交时间： 2017-08-23
摘要： Nonuniform strain fields might induce the segregation of alloying solutes and ultimately lead to the mechanical performance degradation of body-centered-cubic (bcc) Fe based steels serving in extreme environments, which is worthy of investigation. In this paper, two typical volume conserving strains, shear strain (SS) and normal strain (NS), are proposed to investigate the strain effects on solute stabilities in bcc iron by first-principles calculations. For solutes in each transition metal group, the calculated substitution energy change due to SS exhibits a linear dependence on the valence d radius of the solutes, and the slope decreases in an exponential manner as a function of the absolute difference between the Watson’s electronegativity of iron and the averaged value of each transition metal group. This regularity is attributed to the Pauli repulsion between the solutes and the nearest neighboring Fe ions modulated by the hybridization of valence d bands and concluded to be originated from the characteristics of valence d bonding between the transition-metal solutes and Fe ions under SS. For main-group and post transition-metal solutes, the considerable drop of substitution energy change due to NS is concluded to be originated from the low-energy side shift of the widened valence s and p bands of the solutes. Our results indicate that the stabilities of substitutional solutes in iron under volume-conserving strain directly correlate with the intrinsic properties of the alloying elements, such as the valence d radius and occupancy, having or not having valence s and p bands.
分类： 物理学 >> 核物理学 提交时间： 2025-06-07
摘要： In current work, the fission property of ^{180}Hg is investigated based on the Skyrme density functional theory (DFT). The impact of the high-order hexadecapole moment (q_{40}) is found at large deformations. With the q_{40} constraint, a smooth and continuous potential energy surfaces (PES) could be obtained. Especially, the hexadecapole moment constraint is essential to get proper scission configurations. The static fission path based on the PES supports the asymmetric fission of ^{180}Hg. The asymmetric distribution of the fission yields of ^{180}Hg is further reproduced by the time-dependent generator coordinate method (TDGCM), and agrees well with the experimental data.
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