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1.
A molecular dynamics simulation of neutral clusters (H2O)
n ≤ 21 has been performed in the framework of the flexible polarized model. The formation and evolution of the dipole moment of
the cluster have been investigated with a change in the size and temperature of the cluster and an external electric field.
It has been shown that at low electric fields corresponding to the experiments on the deflection of clusters in the transverse
inhomogeneous electrostatic field (Moro et al., 2006), the induced polarization of the cluster is determined by the orientational
polarizability of the “rigid” cluster, rather than by the intracluster reorientation of the molecules. The calculated dependence
of the effective polarizability of the cluster in the low field on n qualitatively reproduces the experimental results, but the calculated polarizability is numerically much higher than the
experimental value by, e.g., a factor of 4 for n ≈ 20. 相似文献
2.
里德堡原子由于具有体积大、寿命长、易极化及在外电场中能级易于操控等特点, 已经成为了目前物理学领域研究的热点之一. 本文在磁光阱中实验测量了铯原子15P3/2和16P3/2态的Stark光谱,根据光谱给出了15P3/2和16P3/2|m|=1/2 Stark态在0-1400 V/cm场强范围适用的Stark 能量和偶极矩的经验性解析表达式; 用数值方法求解薛定谔方程获得了这些态的Stark能量、偶极矩和电子几率密度分布. 电子几率密度分布定性说明了计算的偶极矩矢量的方向是正确的. 计算的Stark能量、偶极矩与实验结果相一致. 相似文献
3.
L. Zhang W. Kleemann J. Dec R. Wang M. Itoh 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):163-171
The dielectric permittivity ε′ - i
of SrTi 18O 3 (STO18) is studied under a dc electric field E as a function of the temperature, T. In ε′
vs.
T, a double-peak is found when 0 < E < 30 KV/m. While the peak at high-T is attributed to the smeared ferroelectric phase transition, the low-T one is induced by domain wall motion. The transverse Ising model including an external homogeneous and quenched random-fields
is successfully used to describe both the smeared phase transition and the domain wall response in the low-T domain state. The calculations are in good agreement with the experimental results.
Received 4 January 2002 / Received in final form 25 March 2002 Published online 19 July 2002 相似文献
4.
O. V. Ivanov D. A. Shport E. G. Maksimov 《Journal of Experimental and Theoretical Physics》1998,87(1):186-199
First-principles calculations are performed relating to the stability of a series of perovskite crystals with respect to transition
to the ferroelectric and the antiferroelectric state. The calculations employ the generalized Gordon-Kim method, in which
the total charge density of an ionic crystal is represented as a superposition of the densities of the individual ions. In
the spirit of the nonequilibrium thermodynamics of Leontovich the charge density of an individual ion is calculated in the
presence of external auxiliary fields which deform this density. Multipole deformations up to quadrupole are taken into account.
The actual magnitude of the deformation is found by minimizing the total energy of the crystal in the Thomas-Fermi-Dirac approximation.
The calculated values of the ion shifts in the ferroelectric phase for BaTiO3, and also the electron contribution to the dielectric constant ε
∞ and the dynamic Born effective charges Z
eff are found to be in good agreement with the experimental data. The proposed method allows one to obtain an analytical expression
for ε
∞, Z
eff, and the dynamic vibration matrix. It is shown that these expressions formally coincide with the expressions arising in the
phenomenological models of the polarized and deformed ion. Analysis of the expressions obtained confirms the validity of the
classical theory of ferroelectrics of displacement type for perovskite crystals.
Zh. éksp. Teor. Fiz. 114, 333–358 (July 1998) 相似文献
5.
G. Regenfus 《Zeitschrift für Physik A Hadrons and Nuclei》1974,269(3):259-263
Measurements of the spin polarization of field emitted electrons from various ferromagnetic (Gd, Ni, Fe) and nonferromagnetic metals (W) show a steady increase of the angle? s between momentum and electron spin with increasing external magnetic field (spin rotation). This effect is refered to the coupling between the magnetic moment of the electron and the strong electric field in the potential barrier at the emitter surface during the tunneling process. A formal application of the equation of spin motion derived by Bargmann, Michel and Telegdi for an electron moving in homogeneous electromagnetic fields delivers a quantitative agreement with the experimental results. 相似文献
6.
C. Silva B. Goncalves M. A. Pedrosa C. Hidalgo K. McCarthy E. Calderon J. Herranz I. Pastor O. Orozco 《Czechoslovak Journal of Physics》2005,55(12):1589-1596
Edge polarization experiments were carried out on TJ-II using an electrode. It has been found that the plasma response is
different at densities below and above the threshold value to trigger the spontaneously development of E × B sheared flows. At low densities, the edge plasma potential is fully controlled by external biasing, while at higher densities
it is determined not only by external biasing but also by the electric fields spontaneous developed. Although an improvement
in particle confinement is observed for both polarities, a larger increase is observed for negative electrode bias.
Presented at the Workshop “Electric Fields, Structures and Relaxation in Edge Plasmas”, Tarragona, Spain, July 3–4, 2005. 相似文献
7.
S. Ağduk G. Gökoğlu 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,79(4):509-514
We present the results of ab initio calculations of lattice dynamics and the second order
elastic stiffness constants of nickel-based magnetic shape memory alloy Ni2MnIn in
stoichiometric composition. The plane wave basis sets and pseudopotential
method within spin-polarized generalized gradient approximation (σ-GGA) scheme of the density functional theory (DFT) is applied. Elastic
constants are calculated by tetragonal and monoclinic isochoric strains
on cubic L21 structure. The calculated elastic constants
agree very well with the recent ultrasonic experimental data. Phonon dispersion spectra are investigated within linear response
technique
of the density functional perturbation theory (DFPT). A vibrational anomaly is observed in phonon spectra at the transverse
acoustic mode (TA2) in [ζ
ζ0]
direction at wavevector ζ = 0.3 as an indication of the structural instability of the system to shear deformation. This anomaly is also verified by
the
low shear modulus and large elastic anisotropy ratio. Phonon dispersion curves are in excellent agreement with the results
of recent neutron diffraction experiments. 相似文献
8.
Processes of electron trapping and detrapping determine in many respects intense processes arising in dielectric and delayed
by 1–100 ns from the irradiation pulse of a high-power electron beam, such as electron emission, electric discharge in the
bulk of the dielectric, flashover, and electric breakdown. A model of charged donor center ionization in a dielectric exposed
to a strong electric field is constructed. The model takes into account 1) the energy spectrum of the charged donor center
in the dielectric, 2) the semiclassical state density in the donor center, 3) spontaneous emission of phonons by the electron
localized in the donor center, 4) increase in the kinetic energy of the electron (heating) in the external electric field,
5) electron tunneling through a potential barrier and its reflection from the barrier depending on the external field intensity,
and 6) thermal fluctuations of energy of the electron localized in the donor center. The probability of charged donor center
ionization in the dielectric per unit time is calculated. In weak fields, the field dependence of the ionization probability
almost coincides with that for the Poole–Frenkel theory. In strong fields, the contribution of electron heating to the external
electric field is the deciding factor.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 10–16, December, 2008. 相似文献
9.
Galina A. Vergunova Sergey Yu. Gus’kov Vladislav B. Rozanov Olga N. Rozmej 《Journal of Russian Laser Research》2010,31(5):509-518
We investigate theoretically the formation of a plasma in a plane layer of polymer foam (density ρ = 0.002 g/cm3 and thickness 800 μm) under the action of an external source of soft X-ray radiation under the conditions of PHELIX experiments. The incident
flux is assumed to have a Planck’s distribution over the spectrum with T
rad = 20–40 eV. In numerical calculations, the flux of incident X-ray radiation and the spectral constants of the target substance
are varied. The action of an external X-ray radiation source on a low-density foam substance with a density of 2 mg/cm3 causes a plasma to be formed with relatively homogeneous profiles of density and temperature T = 15–35 eV. Absorption of externalradiation energy is distributed in the volume. The plasma temperature increases with increase
in the external energy, and the energy passed through the plasma also increases. The results prove to be sensitive to the
values of optical constants used in numeral simulation. The spectral flux of external radiation passed through the plasma
is chosen as a criterion of correctness of the optical constants used in the calculations. In future experiments using the
PHELIX facility, we plan to investigate the slowing-down of an ion beam in a plasma formed as a result of indirect heating
of low-density polymer triacetate cellulose (TAC) foam with densities ρ = 0.001–0.01 g/cm3 under the action of a pulse of X-ray radiation, into which the laser radiation is preliminarily transformed. 相似文献
10.
F. E. Orlenko S. I. Chelkak E. V. Orlenko G. G. Zegrya 《Journal of Experimental and Theoretical Physics》2010,110(5):805-810
Collective effects of spin ordering in a quasi-one-dimensional degenerate electron gas are discussed. The total energy of
the quasi-one-dimensional system, as well as the exchange contribution per particle, has been calculated by the Hartree-Fock
method. It has been shown that spontaneous polarization can be observed in the system when a universal parameter related to
the density of the particles satisfies the inequality r
s
≥ 0.476. A comparative analysis of one-, two-, and three-dimensional systems has been performed. A general expression has
been obtained for the total energy per particle as a function of the degree of polarization and dimension of the system. According
to this expression, the possibility of spontaneous polarization in the system is closely correlated with the dimension of
the system. 相似文献
11.
S. I. Vorob’ev E. I. Golovenchits V. P. Koptev E. N. Komarov S. A. Kotov V. A. Sanina G. V. Shcherbakov 《JETP Letters》2010,91(10):512-517
The magnetic properties of the EuMn2O5 multiferroic (samples consisting of single crystals and ceramic samples) have been investigated by the muon-spin-relaxation
(μSR) method in the temperature range of 10–300 K. Below the magnetic ordering temperature T
N = 40 K, the loss of the polarization of muons and the effect of the external magnetic field have been observed. Both phenomena
can be explained by an additional channel of the depolarization of muons owing to the appearance of muons in a medium with
a low electron density due to the charge separation process (the redistribution of the electron density in the phase transition
process). The “memory” phenomenon has been revealed in a sample in the external magnetic field; the memory relaxation time
depends on the size of the structure units of the samples (single crystals or ceramic grains). 相似文献
12.
Nonlinear optical constants of the alkali metals, responsible for the second harmonic generation, are calculated using the Drude model. It is found that the electric quadrupole term of the nonlinear polarization is larger than that of a previous theory of Jha by a major factor of ω2p/ω2. By considering a more realstic electron density distribution, we also obtain an additional dipole term due to symmetry breakdown at the surface. The new nonlinear polarization gives the reflected second harmonic intensity in good agreement with experiments. 相似文献
13.
It is theoretically shown that in rare gases at P < /100 atm the external electric fields of the order of 100 V/cm could significantly
change the value of electron density in the region of μ- or μ+ stopping point and affect the muonic atoms formation in plasma‐chemical reactions. The kinetic model of processes which might
explain the results of μSR‐experiments for μ- in Ne and Ar both with and without external electric field is proposed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
14.
We present a theoretical analysis of the electronic structure of GaN/AlN quantum dots (QD) with a hexagonal, truncated-pyramidal shape. We use a Fourier-transform technique that we had previously developed to calculate the 3D strain and built-in electric fields due to the QD structure. The electron and hole energy levels and wavefunctions are then calculated in the framework of an 8-band k·P model (with zero spin–orbit splitting), using an efficient plane-wave expansion method. We show that because of the large built-in piezoelectric and spontaneous polarization fields, the calculated transition energy is sensitive to variations in the wetting layer width, pyramid top diameter and also to the values chosen for the piezo-electric constants and spontaneous polarization values of bulk GaN and AlN. Numerical results are presented for a set of GaN/AlN QD structures that have been studied experimentally and described in the literature. We find that the calculated value of the ground-state optical transition energy for these structures is in good agreement with experiment. 相似文献
15.
蒽(anthracene)具有良好的热稳定性以及较高的荧光量子产率的优点, 是最早用于研究有机发光器件(organic light-emitting device, OLED)的材料之一. 在本文中, 主要利用量子化学方法研究了不同外电场对蒽分子激发特性的影响规律. 首先采用密度泛函理论(density functional theory, DFT)在6-311G(d, p)基组水平上对蒽分子基态结构进行优化, 基于稳定基态结构, 利用含时密度泛函(time-dependent density functional theory, TDDFT)以及同一基组水平, 计算出蒽分子的前十个激发态的激发能、跃迁偶极矩、振子强度和紫外吸收光谱等数据. 然后以密度泛函B3P86方法优化出的不同外电场下蒽分子基态结构为基础, 使用TDDFT方法研究了不同外电场对蒽分子前线轨道能级和激发特性的影响规律. 结果显示, 无场时蒽分子在紫外区域234.50 nm处有一个较强的吸收峰, 对应基态电子跃迁至第5激发态吸收光子波长; 在外电场作用下, 蒽分子电子由基态跃迁到激发态的各项光谱参数均有显著变化, 加场后蒽分子的吸收光谱发生了红移, 由紫外波段移向了紫外–可见光波段, 与实验值相符合. 分子前线轨道的计算结果也表明蒽分子的最高占据轨道(highest occupied molecular orbital, HOMO)和最低未占据轨道(lowest unoccupied molecular orbital, LUMO)能量差值在不同电场下存在差异.
关键词:
蒽
外电场
激发特性 相似文献
16.
V. A. Astapenko 《Journal of Experimental and Theoretical Physics》1999,88(5):889-894
The polarization dependence of the stimulated bremsstrahlung and inverse bremsstrahlung (SBIB) of quasiclassical electrons
on highly charged ions with a core is calculated in the approximation of a specified Coulomb current. Emission frequencies
close to an eigenfrequency of the ion core are considered. The contributions of the static and polarization channels are taken
into account in the amplitude of the process. When the nondipole nature of the interaction between the incident particle and
a resonant transition in the ion core is taken into account, interference between these channels causes the spectral-amplitude
characteristics of the process to assume a specific dependence on the angle α between the electric field intensity vector of the electromagnetic wave and the initial velocity vector of the incident particle.
This dependence, which persists after integration of the cross section over the scattering angle of the incident particle,
causes interference effects, viz., asymmetry of the line shape and dips in the dependence of the SBIB cross section on electric
field intensity, to appear for α=π/2 and significantly reduces them for α=0.
Zh. éksp. Teor. Fiz. 115, 1619–1629 (May 1999) 相似文献
17.
V. V. Gladkii V. A. Kirikov S. V. Nekhlyudov E. S. Ivanova 《Physics of the Solid State》1997,39(11):1829-1834
Slow polarization relaxation of a ferroelectric in a weak electric field is investigated in triglycine sulfate crystals with
different states of the domain structure and surface. An automated setup is described that allows one to register relaxation
with record accuracy. It is shown that under conditions of little change in the “degree of metastability” of the structure,
the variation of the polarization ΔP with time t follows the law ΔP=C/(1+t/ta)n in all cases, where the parameters C, a, and n depend on the state of the structure and the surface. We present a phenomenological analysis of the experimental data based
on the assumption that the nuclei are independent and contribute additively to the total polarization of the crystal, and
construct spectra of the energy barriers of the domain walls. Aspects of the transformation of the spectra with variation
of the nature of the domain structure, depth of surface relief, and magnitude of the external electric field are elucidated.
Fiz. Tverd. Tela (St. Petersburg) 39, 2046–2052 (November 1997) 相似文献
18.
E. A. Akopyan G. B. Nersisyan G. G. Matevosyan 《Radiophysics and Quantum Electronics》1997,40(10):823-826
In this paper we present polarization losses of a charged particle in a Maxwell plasma placed in an external HF electric field
allowing for oscillations under the action of an external field of both the particle and plasma electrons. Deriving the expressions
for particle losses, we assumed that the vector of translational motion of the particleu is directed at an arbitrary angle with respect to the external HF field vector.
Institute of Radiophysics and Electronics, National Academy of Sciences of Armenia, Ashtarak. Translated from Izvestiya Vysshikh
Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 10, pp. 1224–1229, October, 1997. 相似文献
19.
Jérôme Daligault 《Journal of statistical physics》2011,143(6):1189-1246
We present a theory for the construction of renormalized kinetic equations to describe the dynamics of classical systems of
particles in or out of equilibrium. A closed, self-consistent set of evolution equations is derived for the single-particle phase-space distribution function f, the correlation function C=〈δfδf〉, the retarded and advanced density response functions χ
R,A
=δf/δφ to an external potential φ, and the associated memory functions Σ
R,A,C
. The basis of the theory is an effective action functional Ω of external potentials φ that contains all information about the dynamical properties of the system. In particular, its functional derivatives generate
successively the single-particle phase-space density f and all the correlation and density response functions, which are coupled through an infinite hierarchy of evolution equations.
Traditional renormalization techniques (involving Legendre transform and vertex functions) are then used to perform the closure
of the hierarchy through memory functions. The latter satisfy functional equations that can be used to devise systematic approximations
that automatically imply the conservation laws of mass, momentum and energy. The present formulation can be equally regarded
as (i) a generalization to dynamical problems of the density functional theory of fluids in equilibrium and (ii) as the classical
mechanical counterpart of the theory of non-equilibrium Green’s functions in quantum field theory. It unifies and encompasses
previous results for classical Hamiltonian systems with any initial conditions. For equilibrium states, the theory reduces
to the equilibrium memory function approach used in the kinetic theory of fluids in thermal equilibrium. For non-equilibrium
fluids, popular closures of the BBGKY hierarchy (e.g. Landau, Boltzmann, Lenard-Balescu-Guernsey) are simply recovered and
we discuss the correspondence with the seminal approaches of Martin-Siggia-Rose and of Rose and we discuss the correspondence
with the seminal approaches of Martin-Siggia-Rose and of Rose. 相似文献
20.
The nonrelativistic and relativistic energy eigenvalues of the electron in the inhomogeneous magnetic fieldH
z
=Hr
−1,r=(x
2 +y
2)1/2 are derived in a form displaying the explicit spin dependence. The possibility of magnetic hydrogen atom formation and the
spontaneouse
+
e
− pair creation following from these eigenvalues is mentioned. The expressions for pressure, energy, particle number and magnetic
moment of an electron gas in this IMF are calculated in the degenerate limit. The possibility of spontaneous magnetisation,i.e., ferromagnetic behaviour, is established. Further, the pressure of the electron gas in the same type of fields is an order
of magnitude higher than those in a homogeneous magnetic field and crossed homogeneous electric and magnetic fields for comparable
field strengths. 相似文献