低温氩等离子体中的单探针和发射光谱诊断技术

使用静电探针和发射光谱分析方法，测量了实验室圆柱形辉光等离子体轴向I-V曲线和发射光谱.通过电子能量概率函数方法、Fermi-Dirac模型、低气压放电的Schottky扩散理论，分别计算了等离子体的电子温度、电子激发温度和电子密度.研究了利用等离子体发射光谱计算电子激发温度、低气压放电理论估算电子密度的方法与静电探针诊断方法的内在联系，讨论了不同方法的使用特点.所研究的方法在某些特殊环境的等离子体参数诊断中具有较好的参考和应用价值. 关键词： 静电探针 发射光谱 电子能量概率函数 Fermi-Dirac模型     

基于路径积分的声传播微观特性的研究

运用量子力学的Feynman路径积分理论,尝试研究空气中声传播的计算方法及其微观特性。选取一小团空气(小体元)为研究对象,将声传播过程中一列振动的空气小体元近似为一组谐振子集合,用路径积分方法给出系统的能量方程及波函数,研究并分析声传播的某些机制和它的微观特性。在量子分子状态下,用密度矩阵将系统概率波幅(跃迁幅)与配分函数相关联,给出了谐振子处于能量E_n的概率p(E_n)和能量的平均值(?)。     

名词浅释

电子简并态,费米电子气 最早人们曾以为在金属(或等离子体)中自由电子的性质类似于理想气体,其后发现它们和理想气体有很大的差别:它们遵从泡利不相容原理和费米-狄拉克统计规律;也就是说,即使温度降到绝对零度时,它们也不会静止,而是按一定能级分布直到某一最大能量E0为止.这种状态称为电子的完全简并态。具有这种能量分布的电子“气体”一般称为“费米电子气”. 实际上,上述简并态并不仅在低温下才出现.理论表明,只要电子总数N和其所占的总体积V以及温度T之间存在 的关系,电子就可进入高度简并态〔式中K为玻耳兹曼官数,h为普朗克常数,m…     

非晶碳结构建模和电子结构的第一性原理研究

基于密度泛函理论,采用了一种更为精确的交换相关泛函OLYP(OPTX+LYP),对密度范围从2.0到3.2 g/cm³的非晶碳进行结构建模. 模拟得到的5个碳网络结构无论从径向分布函数还是sp³含量都与实验符合得很好. 对非晶碳电子结构的研究表明费米能级附近的电子态密度主要是sp²碳原子的贡献. 随着密度的增加,sp³碳原子增加,费米能级附近的态密度越来越小. 小环结构增加了费米能级附近的电子态密度,缺陷态在费米能级形 关键词： 非晶碳 密度泛函理论 电子结构     

强光场中电子系统与多光子的相互作用

在非相对论量子场论框架下,给出电子场和光子场相互作用时整个系统的哈密顿量H_tot,研究在强光场中非线性项即A²项的作用.电子系统用Fermi-Dirac统计的Schr?dinger量子波场描述.采用“自洽平均场”和“有效质量”近似,并基于位移谐振子的相干态方法,得到电子波光量子场算子函数的Lee-Low-Pines表式f(b⁺),再利用算子函数f(b⁺)对算子b+的微商公式,导出了相关理论计算公式,其中包括电子能量E< 关键词： 强光场 多光子 非线性光学     

双价原子的简单组态相互作用理论

详细分析一种简单的非变分式的组态相互作用理论,用于研究双价原子系统。用这种理论精确求解该系统的多组态状态波函数及其相应的能量本征值,并定量地分析组态之间的相互作用,它反映了电子之间的交换作用和相关作用.使用一组由B-spline构成的近乎完全的有限基函数,可以有效地考虑到被限制在有限体积内的正能量单电子轨道对连续区所作的贡献。具体计算典型的双价原子-Be原子,所得结果和实验数据相比较,符合得很好.     

势场作用下粒子的双缝干涉现象分析

根据费曼路径积分原理,定量分析了势场作用下粒子的双缝干涉实验,分别得到谐振子势和线性势下粒子的干涉强度分布公式,并对两种势场下的干涉条纹作了分析.指出谐振子势下粒子的双缝干涉受势场角频率控制,线性势下干涉条纹主极大发生位移.最后,由路径积分的计算过程分析得知,双缝的形状决定强度分布公式,与波动光学的分析结果一致.     

密度矩阵对π-核光学位中泡利修正项的影响

π-核光学位中的泡利修正项与密度矩阵密切相关.本文分别用均匀费米气体模型、定域费米气体模型、修正的定域费米气体模型和壳模型谐振子波函数计算了O~(18)的密度矩阵,并由此研究了在△_(33)共振区(π分子动能为50～300MeV的区域)二级π-核光学位中的泡利修正项.对四种情况进行了分析、比较.     

量子阱中二维电子气的性质

利用提出的三维不对称方势阱模型，对半导体量子阱中二维电子气的性质进行了研究，确定其量子能级和费米能量，并对有关结果进行了讨论。     

推广的Glauber理论及其在晕核散射中的应用

介绍了推广到晕核散射的Glauber理论,并用其研究晕核¹⁴Be的散射问题.弹核的密度分布分别采用谐振子密度分布和相对论平均场理论计算得到具有两个晕中子结构的密度分布,对晕核模型的多重积分采用蒙特卡洛数值积分方法.计算了不同能量下¹⁴Be,¹²Be与靶核¹²C散射的反应截面,并与实验结果进行比较,¹⁴Be的两个中子采用具有晕中子密度分布的理论计算与实验符合较好,而采用不具有晕中子密度分布的结果与实验值相差较大.     

Metastable systems driven by colored noise: The stationary state

The influence of the Bardeen-Herring back-jump correlations on the Fermi-Dirac statistics of the one-dimensional nonhomogeneous fermionic lattice gas is studied by the Monte Carlo simulation technique and semianalytically. The resulting distribution is obtained, exhibiting increased population of the lower levels in comparison to the Fermi-Dirac statistics.     

Feynman integral and perturbation theory in quantum tomography

We present a definition for tomographic Feynman path integral as representation for quantum tomograms via Feynman path integral in the phase space. The proposed representation is the potential basis for investigation of Path Integral Monte Carlo numerical methods with quantum tomograms. Tomographic Feynman path integral is a representation of solution of initial problem for evolution equation for tomograms. The perturbation theory for quantum tomograms is constructed.     

Beyond the mean-field: Quantum Monte Carlo approach for finite fermi systems

Large-amplitude fluctuations around the mean-field are important in hot finite Fermi systems. In the quantum Monte Carlo approach these fluctuations are taken into account exactly but often lead to a sign problem. A practical solution to the sign problem in the framework of the nuclear shell model allows realistic calculations in model spaces that are much larger than those that can be treated by conventional diagonalization methods. Recent applications of the Monte Carlo methods for microscopic calculations of collectivity and level densities in heavy nuclei are presented. Presented at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September 1–5, 1997. This work was supported in part by the Department of Energy grant No. DE-FG-0291-ER-40608.     

Thermodynamics and structure of a two-dimensional asymmetric electrolyte by integral equation theory

Integral equation theories and Monte–Carlo simulations were used to determine the thermodynamic and structural properties of a two-dimensional asymmetric Coulomb system. We check correctness of different closures in integral equations and their ability to reproduce Kosterlitz–Thouless and vapour–liquid phase transitions of the electrolyte and critical points. Integral equation theory results were compared with Monte–Carlo data. Among selected closures, hypernetted-chain approximation results matched computer simulation data best, but these equations unfortunately break down at temperatures well above the Kosterlitz–Thouless transition. The Kovalenko-Hirata closure produces results even at very low temperatures and densities, but no sign of phase transition was detected.     

A phase-space particles motion scheme for electron kineticsimulation

A phase-space particle motion scheme (PSPMS) for electron kinetic simulation is proposed. This scheme is based on the convenient representation of electron motion in phase space using the particles method. PSPMS offers the possibility of calculating the electron energy distribution function (EEDF) much faster than by conventional methods. PSPMS electron calculation is shown to match convective scheme and Monte Carlo simulations of swarms in the uniform electric field and the cathode fall (CF). PSPMS may be used for a self-consistent model of low-pressure glow discharge construction     

Thermodynamics of the uniform electron gas: Fermionic path integral Monte Carlo simulations in the restricted grand canonical ensemble

The uniform electron gas (UEG) is one of the key models for the understanding of warm dense matter—an exotic, highly compressed state of matter between solid and plasma phases. The difficulty in modelling the UEG arises from the need to simultaneously account for Coulomb correlations, quantum effects, and exchange effects, as well as finite temperature. The most accurate results so far were obtained from quantum Monte Carlo (QMC) simulations with a variety of representations. However, QMC for electrons is hampered by the fermion sign problem. Here, we present results from a novel fermionic propagator path integral Monte Carlo in the restricted grand canonical ensemble. The ab initio simulation results for the spin-resolved pair distribution functions and static structure factor are reported for two isotherms (T in the units of the Fermi temperature). Furthermore, we combine the results from the linear response theory in the Singwi-Tosi-Land-Sjölander scheme with the QMC data to remove finite-size errors in the interaction energy. We present a new corrected parametrization for the interaction energy and the exchange–correlation free energy in the thermodynamic limit, and benchmark our results against the restricted path integral Monte Carlo by Brown et al. [Phys. Rev. Lett. 110 , 146405 (2013)] and configuration path integral Monte Carlo/permutation-blocking path integral Monte Carlo by Dornheim et al. [Phys. Rev. Lett. 117 , 115701 (2016)].     

Exchange monte carlo for molecular simulations with monoelectronic hamiltonians

We introduce a general Monte Carlo scheme for achieving atomistic simulations with monoelectronic Hamiltonians including the thermalization of both nuclear and electronic degrees of freedom. The kinetic Monte Carlo algorithm is used to obtain the exact occupation numbers of the electronic levels at canonical equilibrium, and comparison is made with Fermi-Dirac statistics in infinite and finite systems. The effects of a nonzero electronic temperature on the thermodynamic properties of liquid silver and sodium clusters are presented.     

Bold diagrammatic Monte Carlo technique: when the sign problem is welcome

We introduce a Monte Carlo scheme for sampling a bold-line diagrammatic series specifying an unknown function in terms of itself. The range of convergence of this bold(-line) diagrammatic Monte Carlo (BMC) technique is significantly broader than that of a simple iterative scheme for solving integral equations. With the BMC technique, a moderate "sign problem" turns out to be an advantage in terms of the convergence of the process. For an illustrative purpose, we solve the one-particle s-scattering problem. As an important application, we obtain the T matrix for a Fermi polaron (one spin-down particle interacting with the spin-up fermionic sea).     

On electron screening effects in the low-energy 3He(d,p)4He data

We have calculated the screening effects of the two electrons in the atomic ³He gas target on the low-energy³He(d, p)⁴He data. The nuclear degrees of freedom have been described within the microscopic multi-channel Resonating Group Method, while the two electrons have been treated in Born-Oppenheimer approximation deriving the exact screening potential within the Path Integral Monte Carlo method. Our model underestimates the observed screening effects implying the need to consider the coupling of nuclear and electronic degrees of freedom.     

Effects of a small deviation from fermi statistics

By considering a generalized statistics with occupation numbers between Bose-Einstein and Fermi-Dirac statistics we study the resultant distribution when the states differ by a small factor from a Fermi-Dirac distribution. Both the Fermi energy and any level crossing phenomena are sensitive to such statistics; in particular, the electrical conductivity and the free electron heat capacity of fermions at low temperatures receive corrections due to alterations of Fermi-Dirac statistics.