The influence of defects on magnetic properties of fcc-Pu

The influence of vacancies and interstitial atoms on magnetism in Pu is considered in the framework of the density functional theory. The crystal structure relaxation arising due to various types of defects is calculated using the molecular dynamics method with a modified embedded atom model. The local density approximation with explicit inclusion of Coulomb and spin-orbit interactions is applied in matrix invariant form to describe correlation effects in Pu with these types of defects. The calculations show that both vacancies and interstitials give rise to local moments in the f-shell of Pu in good agreement with experimental data for aged Pu. Magnetism appears due to the destruction of a delicate balance between spin-orbit and exchange interactions.     

Density-functional calculations of alpha, beta, gamma, delta, delta', and epsilon plutonium

Total energies for the six known polymorphs of plutonium metal have been calculated within spin and orbital polarized density-functional theory as a function of lattice constant. Theoretical equilibrium volumes and bulk moduli correspond well with experimental data and the calculated total energies are consistent with the known phase diagram of Pu. It is shown that a preference for the formation of magnetic moments, increasing through the alpha-->beta-->gamma phases, explains their position in the ambient pressure phase diagram and their anomalous variation of atomic density. A simple model is presented that establishes a relationship between atomic density, crystal symmetry, and magnetic moments which is universally valid for all Pu phases.     

Ground state theory of delta-Pu

Correlation effects are important for making predictions in the delta phase of Pu. Using a realistic treatment of the intra-atomic Coulomb correlations we address the long-standing problem of computing ground state properties. The equilibrium volume is obtained in good agreement with experiment when taking into account Hubbard U of the order 4 eV. For this U, the calculation predicts a 5f(5) atomiclike configuration with L = 5, S = 5/2, and J = 5/2 and shows a nearly complete compensation between spin and orbital magnetic moments.     

A note on moments of limit log-infinitely divisible stochastic measures of Bacry and Muzy

A multiple integral representation of single and joint moments of the total mass of the limit log-infinitely divisible stochastic measure of Bacry and Muzy (Commun Math Phys 236:449–475, 2003) is derived. The covariance structure of the total mass of the measure is shown to be logarithmic. A generalization of the Selberg integral corresponding to single moments of the limit measure is proposed and shown to satisfy a recurrence relation. The joint moments of the limit lognormal measure, classical Selberg integral with \(\lambda _1=\lambda _2=0,\) and Morris integral are represented in the form of multiple binomial sums. For application, low moments of the limit log-Poisson measure are computed exactly and low joint moments of the limit lognormal measure are considered in detail.     

Moments of inertia of fissioning isomers

The moments of inertia of ground states and fissioning isomers of ²³⁶U and ²⁴⁰Pu are calculated within the cranking model by modifying the pairing interaction. In both cases the measured and calculated values agree if the pairing strength is independent of the surface area.     

Spectroscopic properties of 237,239Pu fission isomers from self-consistent calculations

We have studied ^237,239Pu isomeric states: energy levels, M1 and E2 spectroscopic moments and reduced transition probabilities have been calculated within the rotor+quasi-particle model from self-consistently determined single-particle states. The electromagnetic properties of these states have been especially investigated. Without any ad hoc parameter adjustment, a very good reproduction of most of the known spectroscopic data is yieldedwhich assesses the predictive power of the whole approach.     

CN~+离子电子结构和跃迁性质的理论研究

采用多组态参考相互作用方法和AV5Z-DK基组对CN~+离子的两个解离极限C~+(~2P_u)+N(~2D_u)和C~+(~2P_u)+N(~4S_u)下的X~1Σ~+、a~3Π、~1Δ和A~1四个电子态的势能曲线、永久偶极矩和振动能级进行了计算.为保证计算结果的精确性,在计算中考虑了Davidson修正.基于求得的势能曲线,数值求解一维径向薛定谔方程得到了各个电子态的光谱数据,并与实验值和已有的理论值吻合较好.除此之外,对A~1Π→X~1Σ~+和1~1Δ?A1~Π的跃迁性质进行了研究,同时通过跃迁的弗兰克-康登因子及辐射寿命,对CN~+离子激光冷却的可行性进行了分析.     

Antiferromagnetism and correlation of electrons in a one-band Hubbard model

The effect of electron correlations on the antiferromagnetic ground state of the oneband Hubbard model is examined. The ground state is found analytically for a rectangular density of states. The region of ordered states is reduced as compared with the mean-field results due to formation of local moments and suppression of charge fluctuations with increasing Coulomb interaction between electrons. Local moments present in the paramagnetic phase have almost the same values as those existing in the antiferromagnetic one. For a half-filled band antiferromagnetism is not destroyed by correlation effects in the limit of weak interactions.On leave of absence from the Institute of Physics, Jagellonian University, Cracow, Poland     

Pion effects on nuclear magnetic moment and transitions

The present evidence for pion contributions to magnetic moments, transitions and form factors is selectively reviewed with emphasis on the crucial evidence for specific effects. The theoretical basis will be discussed with special emphasis on the physical picture which emerges in the long wavelength limit.     

An investigation of the properties of single-particle states in the second minimum of 237Pu

In connection with the recent measurement of the magnetic moments of the fission isomeric states in ²³⁷Pu, we investigate the following subjects: (i) The spin alignment of the lowest-lying states in a potential minimum which are populated by (α, 2nγ) reactions, and the fragment angular distributions in fission from isomeric states. (ii) The single-particle level scheme in a very deformed Woods-Saxon potential. (iii) The spin polarizability as a function of the quadrupole deformation.     

Long wavelength density fluctuations in supercooled liquids

Long wavelength density fluctuations in a classical liquid are discussed in terms of a model which has the correct small frequency behaviour and the correct high frequency limit, neglecting thermal relaxation effects. Moreover, the first three frequency moments are correct, so that the model should be well suited for the interpretation of inelastic neutron scattering experiments on supercooled liquids.     

Central Limit Theorems for Linear Statistics of Heavy Tailed Random Matrices

We show central limit theorems (CLT) for the linear statistics of symmetric matrices with independent heavy tailed entries, including entries in the domain of attraction of α-stable laws and entries with moments exploding with the dimension, as in the adjacency matrices of Erdös-Rényi graphs. For the second model, we also prove a central limit theorem of the moments of its empirical eigenvalues distribution. The limit laws are Gaussian, but unlike the case of standard Wigner matrices, the normalization is the one of the classical CLT for independent random variables.     

On the black hole limit of rotating discs and rings

Solutions to Einstein’s field equations describing rotating fluid bodies in equilibrium permit parametric (i.e. quasi-stationary) transitions to the extreme Kerr solution (outside the horizon). This has been shown analytically for discs of dust and numerically for ring solutions with various equations of state. From the exterior point of view, this transition can be interpreted as a (quasi) black hole limit. All gravitational multipole moments assume precisely the values of an extremal Kerr black hole in the limit. In the present paper, the way in which the black hole limit is approached is investigated in more detail by means of a parametric Taylor series expansion of the exact solution describing a rigidly rotating disc of dust. Combined with numerical calculations for ring solutions our results indicate an interesting universal behaviour of the multipole moments near the black hole limit.     

The sixth frequency moments for an anisotropic paramagnet with exchange-bond dilution

The sixth frequency moments of the spin correlation function for a bond-diluted anisotropic Heisenberg paramagnet in the high temperature limit are evaluated for arbitrary spin values. Results for both the transverse and longitudinal moments are presented for a model in which the transverse and longitudinal exchange bonds can fluctuate independently. The results are presented in a form which allows the moments for the undiluted, site diluted, and single-bond diluted moments to be also written down.     

Statistical properties of many-particle spectra

Many-particle eigenvalue densities, generated by k-body interactions in asymptotically large spectroscopic spaces, are studied in terms of the density moments of a Gaussian orthogonal ensemble of such interactions. It is shown that the densities approach Gaussian as particle number increases; the rate of approach is determined, as is the rate of departure from the semicircular form which obtains in the few-particle limit, as well as the low-moment representation for intermediate cases. By considering the variances of the moments it is shown that a convergence in probability of the individual densities to the ensemble-averaged density, first demonstrated by Grenander for the fewparticle limit, is valid in general. In part as a preliminary to a study of the density and spectrum fluctuations, explicit forms are derived for the covariances of low-order moments for arbitrary particle number and of moments of general order in the few-particle and many-particle limits. In the limiting cases the ensemble eigenvalue densities are exhibited in terms of a set of statistically uncorrelated Chebyshev or Hermitepolynomial excitations of the ensemble-averaged densities. Some explicit results for GOE fluctuations are given.     

量子分子动力学模拟液体钚的输运性质

采用第一原理分子动力学（QMD）方法模拟液体钚的输运性质.计算的粘性和扩散系数在较低温度时与文献有明显差异,在实验测量范围内,模拟结果与实验一致,温度升高时数值模拟结果趋于一致.利用QMD的模拟结果计算了应力自相关函数和速度自相关函数,结果表明：在温度较低时,液体钚呈现明显的强关联特性.对于具有强关联特性的液体,利用较短时间的QMD模拟结果,通过简单e指数拟合外推到t→∞得到的扩散系数和粘性具有较大偏差,这是造成本文模拟结果与文献结果出现差异的主要原因.通过增加QMD模拟时间步数,获得了更为准确的输运性质.     

Maximum entropy approach to the coupled quadrupole system

The spectral functions of the spin pair correlation functions in a coupled quadrupole system are evaluated using the maximum entropy formalism starting from the exact derivation of the frequency moments to fourth order at the high temperature limit. The numerical computations are carried out for different wave vectors and ratios of the anisotropic field to the quadrupolar interaction. The effects of these parameters on the spectral function are discussed.     

The relativistic equation of state of actinide metals and compounds

Abstract

The effect of spin-orbit coupling upon the calculated pressure-volume relationship is summarized. It is shown that the main effect is to increase the lattice constant, especially in Pu systems. The both measured and calculated pronounced minimum in the lattice constants of the Anlr₂ laves phase compounds at Nplr₂ is also discussed. One influence of spin-orbit coupling upon the magnetic equation of state is shown to be suppression of magnetism. Again the effects are particularly large in Pu systems. The foregoing is illustrated by a relativistic Stoner theory which explains well the absence of magnetism in Np metal and in several Pu compounds.     

Pu或Am含量对铀基混合氧化物的结构和能量及力学性质的影响

U-Pu和U-Am混合氧化物中的Pu或Am含量对核反应堆燃料的高效循环利用至关重要.研究铀基混合氧化物中不同Pu或Am的含量对其结构、力学性质和能量的影响有助于理解和预测提高反应堆中燃料的行为以及与包层的化学或力学相互作用.本文通过DFT+U方法首先探索UO₂、PuO₂和AmO₂的结构和能量随U的变化关系,然后研究UO₂结构中不同Pu或Am含量对其结构和力学性质以及能量的影响.结果表明在UO₂结构中掺入不同Pu或Am的含量均使得体系晶格参数收缩,且与实验观测(U, Pu)O₂中Pu的含量结论是一致的.从能量角度观察,UO₂结构中掺入不同Pu或Am的含量使得体系形成能随掺入量的变化趋势明显不同.结果显示当UO₂结构中掺入Pu为25%时,U-Pu混合氧化物体系的形成能最低,而当UO₂结构中掺入Am为75%时,U-Am混合氧化物体系的形成能最低.此外,我们也探讨和分析了在UO₂