准一维体系的电子关联函数

对于具有库仑相互作用的准一维电子体系,本文根据电子气的集体振荡行为给出了该体系的多体波函数,并由此求出了准一维体系的电子关联函数g(|z₁₂|)。 关键词：     

Instability of layered quantum liquids: 1. Local-field correction in superlattices

For a superlattice with periodd the Singwi et al. (Phys. Rev.176, 589 (1968)) approach for the local-field correction and the static structure factor is formulated. With two approximations we reduce the resulting three-dimensional integral-equation into a one-dimensional integral-equation. For the local-field correction we present analytical results for small wave numbers and large wave numbers. An expression of Hubbard-typ is derived for the local-field correction. Explicit results for boson superlattices and electron superlattice are given. A charge-density-wave instability in a layered Bose condensate withr _s>r_scd^3/4 is discovered.r _s is the small parameter of the random-phase-approximation. The charge-density-wave instability is due to a many-body anomaly (short-range correlations) in layered structures and is a general property of layered quantum liquids. We find the charge-density-wave instability in a layered electron gas forr _s>r_scd. Double-quantum-well structures are also considered. The effects of a finite well width is calculated. The general implications of the charge-density-wave instability for microscopically layered quantum liquids are pointed out.     

准一维体系的电子关联的变分计算

对于具有库仑相互作用的准一维电子体系,本文提出了一种新的模型,得到了准一维体系的电子有效库仑势形式。在相关基函数理论框架下,根据电子气的集体振荡行为,给出该体系的多体波函数,并得到不同密度的电子体系的关联函数和关联能,本文得到的关联函数是恒正的,且满足归一化条件。     

Anfachung und Dämpfung von Ionisationswellen in MHD-Kanälen und ihr Einfluß auf die effektive elektrische Leitfähigkeit,den effektiven Hall-Parameter und die mittlere Elektronentemperatur

The phase velocity, the amplification rate and the critical Hall parameter are theoretically determined for ionization waves in a weakly ionized plasma streaming across a strong external magnetic field and bearing a current flowing perpendicular to both the magnetic field and the stream velocity. The investigations hold for seeded rare gases at any degree of seed ionization. The critical Hall parameter β_c depends on the degree of ionization, the ionization energy and the temperatures of electron gas T₀ and neutral gas T_g · β_c is always greater than one, if 0 < T₀ — T_g ? T₀ holds. The three-dimensional treatment indicates the existence of waves with a nonvanishing wave vector component in the direction of the magnetic field. The influence of ionization waves on mean current density, mean Hall field intensity and mean electron temperature is determined up to second order terms in the relative fluctuations of the electron temperature. The amplification of ionization waves reduces the effective electric conductivity, the effective Hall parameter and the mean electron temperature compared to the undisturbed state. Similar results are also obtained for steady state homogeneous isotropic turbulence and a special case of axially symmetric turbulence. Furthermore, a component of the electric field in direction or in opposite direction to the magnetic field vector may be generated by non isotropic and non homogeneous turbulence.     

The linewidth of surface states of simple metals

The linewidths (inverse lifetimes) Γ_e-e of Be(0001) and Mg(0001) surface electronic states are calculated as the projection of the imaginary part of the self-energy operator of a quasiparticle onto the state. The screened Coulomb interaction is calculated using a model potential, which takes into account the energy gap in the band structure and a surface state located in this gap. The wave functions and energies of electron states are calculated by a self-consistent film pseudopotential method. It is shown that Γ_e-e essentially depends on the position of the surface state in the Brillouin zone. The difference between the calculated values of Γ_e-e and those obtained in a homogeneous electron gas model is shown to be basically due to transitions from surface bands.     

Plasma Diagnostics Using K‐Line Emission Profiles of Silicon

Modifications of K‐line profiles due to a warm dense plasma environment are a suitable tool for plasma diagnostics. We focus on Si K_α emissions due to an electron transfer from 2P to 1S shell. Besides 2P fine structure effects we also consider the influence of excited and higher ionized emitters. Generally spoken, a plasma of medium temperature and high density (warm dense matter) is created from bulk Si the greater part of atoms is ionized. The high energy of K_α x‐rays is necessary to penetrate and investigate the Si sample. The plasma effect influences the many‐particle system resulting in an energy shift due to electron‐ion and electron‐electron interaction. In our work we focus on pure Si using LS coupling. Non‐perturbative wave functions are calculated as well as ionization energies, binding energies and relevant emission energies using the chemical ab initio code Gaussian 03. The plasma effect is considered within a perturbative approach to the Hamiltonian. Using Roothaan‐Hartree‐Fock wave functions we calculate the screening effect within an ion‐sphere model. The different excitation and ionization probabilities of the electronic L‐shell and M‐shell lead to a charge state distribution. Using this distribution and a Lorentz profile convolution with a Gaussian instrument function we calculate spectral line profiles depending on the plasma parameters. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Width of the quasiparticle spectral function in a two-dimensional electron gas with spin-orbit interaction

The results of an investigation of the width of the electron and hole spectral functions in an isotropic electron gas with the Rashba spin-orbit interaction as a function of the wave vector within the G ⁰ W ⁰ approximation are reported. This kind of electron gas is used to simulate two-dimensional systems formed by electrons in In _x Ga_{1 − x} As layers of various heterostructures and by surface electron states on Au(111). It is demonstrated how the width of the spectral function changes as a result of the spin-orbit interaction and how it depends on the branch index of the energy spectrum split by this interaction.     

Laser wakefield acceleration of short electron bunches

The theory of electron acceleration in a plasma wake wave is developed, and the dependence of the main characteristics of accelerated electron bunches on the wakefield parameters is investigated, It is shown that using a prebunching stage, under proper conditions, the final electron density of a compressed and accelerated bunch can exceed the initial electron beam density by orders of magnitude and that longitudinal bunch compression provides quasi-monoenergetic acceleration to high energies, It is demonstrated that, for an initial electron beam radius smaller than the optimal one for efficient beam trapping, the energy spread of the compressed and accelerated electron bunch and its length can be evaluated by using the simple analytical predictions of a one-dimensional (1-D) theory. The obtained analytical results are confirmed by three-dimensional (3-D) numerical modeling     

Spin–orbit stiffness of the spin‐polarized electron gas

In a spin‐polarized electron gas, Coulomb interaction couples the spin and motion degrees of freedom to build propagating spin waves. The spin wave stiffness S_sw quantifies the energy cost to trigger such excitation by perturbing the kinetic energy of the electron gas (i.e. putting it in motion). Here we introduce the concept of spin–orbit stiffness, S_so, as the energy necessary to excite a spin wave with a spin polarization induced by spin–orbit coupling. This quantity governs the Coulombic enhancement of the spin–orbit field acting of the spin wave. First‐principles calculations and electronic Raman scattering experiments carried out on a model spin‐polarized electron gas, embedded in a CdMnTe quantum well, demonstrate that S_so = S_sw. Through optical gating of the structure, we demonstrate the reproducible tuning of S_so by a factor of 3, highlighting the great potential of spin–orbit control of spin waves in view of spintronics applications. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Systematic theoretical investigation of structure and electronic properties of pure copper and lithium doped copper clusters

The pure copper and lithium-doped copper clusters are studied using the unbiased CALYPSO structure searching method and density function theory to understand the evolution of various structure and electronic properties. Theoretical results show the growth behaviours of doped clusters are organised as follows: Li capped Cu_n clusters or Li substituted Cu_n+1 clusters as well as Cu capped Cu_n-1Li clusters. Moreover, the lowest energy structures of Cu_nLi favour planar structures for n ≤ 3 and three-dimensional structures for n = 4–12. In addition, the calculated averaged binding energies, fragmentation energies and second-order difference of energies exhibit obvious odd–even alternations as cluster size increasing. At last, the highest occupied-lowest unoccupied molecular orbital gaps, molecular orbital energy, magnetic property, natural population analysis, natural electron configurations, electrostatic potential, electron density difference, Infrared and Raman spectra and density of states are also, respectively, operative for characterising and rationalising the electronic properties of doped clusters.     

Collisional excitation among the seven lowest states of TiXII

Collision strengths have been calculated for electron impact excitation of sodium-like TiXII for all 21 transitions amongst its lowest seven states. Configuration interaction wave functions have been used to represent the target states. The standard and no-exchangeR-matrix codes have been used to calculate the contribution of partial waves withL⩽8 andL>8 respectively. Collision strengths are tabulated at selected energies in the range 26 to 50 Ryd. Effective collision strengths are tabulated for electron temperatures in the range logT _e=4.0 to logT _e=6.0, withT _e in K. This is the first detailed calculation on this ion in which the effects of exchange, channel couplings and short-range correlation are taken into account.     

Ⅰ类和Ⅱ类准周期半导体超晶格的电子子带和波函数

本文将包迹函数近似推广用于计算有理数近似下,垂直于超晶格轴的波矢K_⊥不等于零时,准周期半导体超晶格(QSS)的电子子带和波函数,对K_⊥=0的情形,分别计算了Ⅰ类的GaAs/Al_xGa_1-xAs和Ⅱ类的InAs/GaSb QSS的电子子带和波函数,直至代序数m=9和6。对于价带对导带影响强的InAs/GaSb QSS,分别计算了m=5和6时电子子带随K_⊥的变化关系。并提出了利用本文结果计算Ⅰ类的GaAs/Al_xGa_1-xAs QSS带间集体激发的具体方法。     

Application of pseudopotential theory to magnetic semiconductor heterostructures

The results of empirical pseudopotential calculations for the semiconductor compound Cd_1 − xMn_xTe are presented. The effective electron and hole masses obtained from the pseudopotential calculations are then employed in an envelope function approximation, using two different effective mass Hamiltonians to evaluate the transition energies of the excitonic ground state in CdTe– Cd_1 − xMn_xTe quantum wells of variable width. It is shown that in non-magnetic systems it is not possible to utilize exciton energies alone to either distinguish between different model Hamiltonians or to quantify the interface roughness. However, it is shown that the latter can be quantified in magnetic systems via the resulting Zeeman effect.     

A hybrid DFT description of the (0001) surface of americium-I

Using a periodic slab model for the (0001) surface of americium-I (Am-I) and the full-potential linear augmented plane wave (FP-LAPW) plus local basis implementation of hybrid density functional theory (HYB-DFT), we show that with a fraction of 0.40 Hartree-Fock (HF) exchange, the non-magnetic nature of the Am-I surface is well described and the electronic properties are in good agreement with recent photoemission spectroscopy data. The work function and surface energy of the non-magnetic semi-infinite surface are predicted to 3.46 eV and 1.03 J/m², respectively. As a function of slab thickness, the surface properties, namely the surface energy, work function, and slab incremental energy converge after five layers. A five layer slab is thus deemed to be sufficient to very accurately model the adsorption of impurities on the surface and adsorbate-induced changes in the work function. A layer-by-layer examination of the nine-layer non-magnetic slab clearly indicates that the 5f electrons are uniformly localized, that is, the 5f electron localization is independent of the position of the layer.     

The local-field correction for the interacting electron gas: many-body effects for unpolarized and polarized electrons

The local-field correction for the three-dimensional and two-dimensional electron gas is calculated within a three-sum-rule version of the self-consistent approach of Singwi, Tosi, Land and Sjölander. Results for 0:01 < r _s < 100 are given and r _s is the RPA-parameter. Correlation effects are studied for the paramagnetic (unpolarized) state and the ferromagnetic (polarized) state and compared with Monte-Carlo calculations and good agreement is found. We conclude that the pair-correlation function and the correlation energy, if calculated within the three-sum-rule approach, shows a better behavior at large rs than if calculated within the two-sum-rule approach. Using the compressibility sumrule we propose a new analytical form of the local-field correction and we compare the dielectric function with recent Monte-Carlo results. We also discuss some new aspects of the one-dimensional electron gas with short-range interaction.     

Resistance and eigenstates in a tight-binding model with quasiperiodic potential

A one-dimensional tight-binding model on a spatially periodic lattice of lengthN, with quasiperiodic potential strength given by the Fibonacci sequence, is investigated numerically. We elucidate theN-dependence of the resistence and the nature of the wave functions. For energies belonging to the spectrum, the results provide strong evidence for algebraic localization and algebraicN-dependence of the resistance, with a distribution of exponents. Implications for quantum chaos are also discussed.     

Runaway of electrons in dense gases and mechanism of generation of high-power subnanosecond beams

New understanding of mechanism of the runaway electrons beam generation in gases is presented. It is shown that the Townsend mechanism of the avalanche electron multiplication is valid even for the strong electric fields when the electron ionization friction on gas may be neglected. A non-local criterion for a runaway electron generation is proposed. This criterion results in the universal two-valued dependence of critical voltage U _cr on pd for a certain gas (p is a pressure, d is an interelectrode distance). This dependence subdivides a plane (U _cr , pd) onto the area of the efficient electron multiplication and the area where the electrons leave the gas gap without multiplication. On the basis of this dependence analogs of Paschen’s curves are constructed, which contain an additional new upper branch. This brunch demarcates the area of discharge and the area of e-beam. The mechanism of the formation of the recently created atomospheric pressure subnanosecond e-beams is discussed. It is shown that the beam of the runaway electrons is formed at an instant when the plasma of the discharge gap approaches to the runaway electrons is formed at an instant when the plasma of the discharge gap approaches to the anode. In this case a basic pulse of the electron beam is formed according to the non-local criterion of the runaway electrons generation. The role of the discharge gap preionization by the fast electrons, emitted from the plasma non-uniformities on the cathode, as well as a propagation of an electron multiplication wave from cathode to anode in a dense gas are considered.     

Influence of impurities on the band ferromagnetism

The influence of non-magnetic impurities on band ferromagnetism for an electron gas withδ-function interaction is investigated in the framework of the quantum field theory applied to phase transitions. The Hartree-Fock approximation is used for non-zero temperatures. An equation for the magnetizationM and the critical temperatureT F_c is obtained. It is found that the transition temperature is lowered by increasing impurity concentration. There exists a critical concentration which vanishes the ferromagnetism.     

Geometries,stabilities, electronic and magnetic properties of small PdnIr (n = 1–8) clusters from first-principles calculations

The geometrical structures, relative stabilities, electronic and magnetic properties of small Pd_nIr (n = 1–8) clusters have been systematically investigated using density functional theory at the B3PW91 level. The optimised geometries show that the lowest-energy structures of Pd_nIr clusters prefer a three-dimensional configuration. The relative stability of these clusters was examined by analysis of the binding energies per atom, fragmentation energies, the second-order difference of energies and the HOMO–LUMO energy gaps as a function of cluster size. The obtained results exhibit that the Pd₂Ir, Pd₃Ir and Pd₅Ir clusters are more stable than their neighbouring clusters. The energy gap of the Pd₂Ir cluster is the largest of all the clusters (2.258 eV). In addition, the charge transfers, vertical ionisation potentials, vertical electron affinities and chemical hardness were calculated and discussed. The magnetism calculations indicate that the total magnetic moment of Pd_nIr clusters is mainly localised on the iridium atom for Pd_1–6Ir clusters. Meanwhile, the 5d orbital plays the key role in the magnetic moment of the iridium atom.