单参考态微扰理论发散问题的理论研究（英文）

本文对闭壳层和开壳层分子系统由于加入弥散函数导致的单参考态微扰理论的发散问题进行了深入的研究.发现对开壳层系统,微扰能量的振幅随体系自旋多重度的增加而增加.本文利用Feenberg变换来处理微扰理论的发散问题.通过调节Feenberg变换的参数λ来加速微扰序列的收敛性.数值计算表明,存在一个λ值,微扰序列收敛最快.还发现该λ值随着自旋多重度增加而增加.     

Co/CoO双层膜的各向异性磁电阻与交换偏置行为研究

本文系统研究了Co/CoO双层膜的各向异性磁电阻(AMR)与交换偏置行为,并给出了外加微扰场对交换偏置磁锻炼效应恢复程度影响的实验结果.结果表明磁锻炼效应发生后,施加0.15T的倾斜微扰场可致使铁磁畴分裂进而诱导磁锻炼效应的恢复,揭示磁锻炼效应恢复程度与微扰场的角度有紧密关联.在微扰场作用下FM自旋在两个方向分裂,一部分自旋沿微扰场方向,另一部则被冷却场的AFM自旋钉扎住而沿原来方向不变.当微扰场和冷却场夹角大于30°时,FM畴被分裂,磁锻炼效应开始恢复,表明一个磁畴内的铁磁自旋偏离夹角最大为30°,而磁锻炼效应发生后,部分AFM自旋偏离冷却场方向的角度则小于30°,实验结果与相应的理论计算结果一致.此外,恢复程度随微扰场角度的增加而增加,最大恢复程度时角度为90°.同时,磁锻炼效应的恢复增加了交换偏置值,为器件设计提供理论支持,在自旋电子学基础和应用研究方面具有重要的指导意义.     

研究类氦原子基态能量的参数微扰法

考虑了类氦原子中电子对核的屏蔽效应,建立了含有屏蔽效应参数的哈密顿算符,并应用微扰理论研究了类氦原子基态能量.通过参数微扰法计算的类氦原子一级近似基态能量与变分法得到的能量完全相同,比无参数微扰法计算的能量更加接近实验值.参数微扰法为研究多电子原子能级和原子能级精细结构提供了一种新的方法.     

简并基态最陡下降微扰理论

本文证明,Cioslowski所引入的一个全新的量子力学计算方案,非简并基态最陡下降微扰理论,通过按对称性选择合适的零级试探波函数后,可以处理简并基态的微扰分裂问题由于最陡下降微扰理论既避免了通常的其他微扰理论需要对各个基矢量无限求和的或求解一组微分方程的缺陷,又具有逐步迭代改善计算结果的优点,本文引进的计算方案可望在原子分子及其他多粒子体系能级的微扰分裂计算中得到广泛应用。 关键词：     

硼原(离)子内壳激发高自旋态能级和辐射跃迁

采用Rayleigh-Ritz变分方法计算了B原子(离子)内壳层激发高自旋态(~(4,5,6)L,L=S,P)里德伯系列的能量和精细结构劈裂,利用截断变分方法改进非相对论能量,并利用一阶微扰理论计算了相对论能量修正和质量极化效应修正,利用屏蔽的类氢公式计算了量子电动力学效应和高阶相对论效应,从而得到了高精度的组态能量.利用精确计算的波函数,计算了这些高自旋态的电偶极辐射跃迁波长、振子强度和辐射跃迁概率.通过长度规范和速度规范计算的振子强度的一致性证明了本文计算的波函数是精确的.相比其他理论计算结果,本文计算的高自旋态的能级及跃迁波长数据与实验数据符合得更好.对于一些高位的内壳层激发高自旋态,相关的能级和跃迁数据为首次报道,本文的计算结果对相关实验光谱谱线标定具有重要意义.     

对非线性量子场论与激光理论中的微扰谐振梯度算子方法的改进

当微优按Hermite多项式H_k的收敛级数作如下展开时,V(X)=b²X²+Σ_k C_kH_k(b^1/2X), 则可将其微扰梯度算子方法应用于微扰谐振子波动方程的求解中.发现若将Hermite多项式基与二项式系数函数依量子数一起使用,则可大大简化微扰梯度与因子分解函数.因此,在不增加其复杂性的情况下,便可求得任意级微扰的本征值与本征函数的分析表示式.通过计算,本文给出了X的偶性微扰势函数V(X),为了说明如何应用改进后的微扰梯度算子方法,本文重新研究了其势函数为V(x)=x²+λX²/(1+gX²),且g>0时的Schr?dinger方程的求解过程. 关键词：     

QCD微扰理论和原子核(Ⅰ)强子的能级移动和质量差

讨论了禁闭情况下(在强子中)的QCD微扰,由层子—胶子相互作用导出了单胶子交换的等效位。在此基础上用MIT袋模型及高斯型波函数近似计算了强子的能级移动和质量差,并与半经典处理及实验结果相比。结果表明在强子中QCD微扰理论是可行的,半经典处理结果正是微扰计算的最低阶项,由此微扰理论给出了袋模型中处理相互作用的新途径。     

相对论平均场理论中的张量项对自旋-轨道劈裂的影响

在相对论平均场理论中引入同位旋标量-矢量介子ω张量项, 以²⁰⁸Pb为例,研究了张量项对原子核平均势场、介子场、自旋-轨道耦合势、单粒子能级的自旋-轨道劈裂和原子核壳层结构等的影响.结果发现张量项对核子平均势的影响主要表现在原子核的表面.随着张量耦合强度的增加, 自旋-轨道耦合势增强,单粒子能级的自旋-轨道劈裂增大,从而导致原子核单粒子能级的壳层结构发生很大变化,传统幻数所对应的主壳消失, 新的主壳出现.     

吸引费米体系多体微扰级数的收敛性

本文用泛函分析的方法,研究了吸引多费子体系中Wigner和Schr?dinger两种微扰级数的收敛性问题。发现这两种微扰级数的“收敛半径”是相同的,但是收敛与发散的速度是不相等的,我们提供了一个较有用的判据。     

绿宝石晶体自旋二重态对基态能级的影响及Jahn-Teller效应

应用不可约张量方法和群的理论构造了三角对称晶场中考虑自旋 轨道相互作用,自旋 自旋相互作用和自旋 其它轨道相互作用的3d3/3d7态离子的可完全对角化的120阶微扰哈密顿矩阵.利用该矩阵计算了绿宝石晶体的基态能级、零场分裂参量,研究了自旋二重态对基态能级的贡献.理论计算值与实验值相符合,证明二重态对基态的贡献是不可忽略的.在此基础上,进一步研究了自旋 自旋相互作用、自旋 其它轨道相互作用和自旋 轨道相互作用对绿宝石晶体的光谱精细结构和零场分裂参量的影响,发现自旋 自旋和自旋 其它轨道相互作用对绿宝石晶体基态能级和零场分裂参量的影响都是不可忽略的.从而通过理论计算值和实验值的比较,证实了在绿宝石晶体中Jahn Teller效应的存在,它能够对光谱精细结构的分裂提出一些更加合理的解释.     

A rearrangement of the Feenberg perturbation formula and elementary excitation interactions in bose fluids

The Feenberg perturbation energy for two quasiparticle excitations is rearranged to be valid in many-boson systems up to fifth order. Doubly excited states in many particle boson systems are studied using Feenberg perturbation theory. The effective interaction energy between quasiparticles, which is described by “ladder state diagrams” — in Bogoliubov approximation, is obtained. It is then shown that in this case the interaction energy depends on density (pressure) and changes its sign when density increases if the bare two-body potential qualitatively has short range repulsion and longer range attraction.     

Combining spin-adapted open-shell TD-DFT with spin–orbit coupling

The recently proposed spin-adapted time-dependent density functional theory (S-TD-DFT) is extended to the relativistic domain for fine-structure splittings of excited states of open-shell systems. Scalar-relativistic effects are treated to infinite order via the spin-free (sf) part of the exact two-component (X2C) Hamiltonian, whereas the spin–orbit couplings (SOC) between the scalar-excited states are treated perturbatively via an effective one-electron spin–orbit operator derived from the same X2C Hamiltonian. The calculated results for prototypical open-shell systems containing heavy elements reveal that the composite approach sf-X2C-S-TD-DFT-SOC is very promising. The fine-structure splitting of a spatially degenerate ground state can also be described properly by taking a non-degenerate excited state as the reference.     

Spin transport in a one-dimensional anisotropic Heisenberg model

We analytically and numerically study spin transport in a one-dimensional Heisenberg model in linear-response regime at infinite temperature. It is shown that as the anisotropy parameter Δ is varied spin transport changes from ballistic for Δ<1 to anomalous at the isotropic point Δ=1, to diffusive for finite Δ>1, ending up as a perfect isolator in the Ising limit of infinite Δ. Using perturbation theory for large Δ a quantitative prediction is made for the dependence of diffusion constant on Δ.     

Heisenberg spin Hamiltonian through a new Heitler-London approach: Test on the half-filled linear Hubbard model

The Heisenberg spin Hamiltonian constructed from a new Heitler-London method is tested on the half-filled linear Hubbard model. It is found that the Heisenberg Hamiltonian of the new Heitler-London method works well in a much wider parameter range than that of the usual perturbation method does.     

晶体C_3H_7NO_2:VO~(2+)的自旋哈密顿参数及局域结构

在晶体场理论(CF机制)和电荷转移机制(CT机制)的基础上,结合双自旋-轨道耦合参量模型、自旋哈密顿量的高阶微扰公式及晶场能量公式计算得到C_3H_7NO_2:VO~(2+)晶体的自旋哈密顿量(EPR参量)和吸收光谱,及电荷转移跃迁能级.对比只采用CF机制和采用双重机制下的计算结果,发现高价钒离子(V~(4+))掺杂在C_3H_7NO_2晶体中的CT机制对于其EPR参量的影响不能忽略.     

一维自旋轨道模型中自旋-轨道能隙产生机理分析

讨论考虑洪特耦合的两带赫伯德模型得到的一维自旋轨道模型中自旋-轨道能隙的产生.运用SU(4)赝费米子表象下的平均场理论,计算求得价键序参数、准粒子激发谱能隙和自旋、轨道密度-密度关联函数随系统耦合参数变化的结果.随洪特耦合相互作用由零开始增强,系统激发谱能隙逐渐打开,并且系统在参数取值为J₁/J₂=1/3处由具有阻错的无序状态相变到自旋铁磁有序和轨道反铁磁有序的状态.     

High spin chemistry underlying organic molecular magnetism: Topological symmetry rule as the first principle of spin alignment in organic open-shell systems of π-conjugation and their ions

This review paper deals with an overview of molecule-based magnetism as a rapidly developing interdisciplinary field, topological symmetry rule as the first principle of spin alignment in organic open-shell systems in the ground state, the proposal of organic through-bond 1D and 2D ferro- and superparamagnets and the detection of the first organic high-spin molecule, m-phenylenebis(phenylmethylene) in the quintet ground state (S = 2), followed by extended organic high-spin systems with π-conjugation such as aromatic hydrocarbons having S = 3, 4, 5. The paper also describes a theoretical approach to the understanding of electronic spin structures of organic high-spin molecules by invoking both Heisenberg and Hubbard model Hamiltonians, weakly interacting intramolecular high-spin systems from both experimental and theoretical sides, the spin density distribution of the first organic high-spin molecule in terms of electron- nuclear multiple resonance spectroscopy and the detection and characterization of ionic high-spin hydrocarbons, emphasizing the establishment of high spin chemistry underlying organic molecular magnetism.     

E.P.R. evidence for the structuring effect of alcohol in water

A computational scheme for frequency-dependent polarizabilities of open-shell systems by coupled Hartree-Fock perturbation theory is presented. It allows the simultaneous approximate prediction of the involved electronic transition energies and can trivially be extended to imaginary values of the frequency. As a simple application, the dipole polarizability and some related properties of Li atoms are evaluated, the agreement with previous estimates being excellent.     

Emergence of U(1) symmetry in the 3D XY model with Zq anisotropy

We study the three-dimensional XY model with a Zq anisotropic term. At temperatures T相似文献