共查询到20条相似文献,搜索用时 31 毫秒
1.
Three-dimensional quasi-equilibrium configurations of a complex (dusty) plasma in narrow channels are investigated using the molecular dynamics simulations for various confining potentials (confinements). The dynamics of the microparticles is described within the framework of a Langevin thermostat with allowance for the pair interaction between charged particles, which is described by a screened Coulomb potential (Yukawa potential). Two confinements—the parabolic potential and hard elastic wall—are considered. It is shown that the confinement strongly affects the crystallization and the local order of the microparticles in the system under consideration; in particular, the appearance of a new quasicrystalline phase induced by the hard wall confinement is revealed. 相似文献
2.
The Hubbard model is a prototype for strongly correlated electrons in condensed matter, for molecules and fermions or bosons in optical lattices. While the equilibrium properties of these systems have been studied in detail, the excitation and relaxation dynamics following a perturbation of the system are only poorly explored. Here, we present results for the dynamics of electrons following nonlinear strong excitation that are based on a nonequilibrium Green functions approach. We focus on small systems—“Hubbard nano‐clusters”—that contain just a few particles where, in addition to the correlation effects, finite size effects and spatial inhomegeneity can be studied systematically. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
3.
A change in the local order of a bounded complex (dusty) plasma in the process of its crystallization and melting has been
examined by molecular dynamics simulations. The dynamics of microparticles is considered in the framework of a Langevin thermostat,
the pair interaction between charged particles is described by a screened Coulomb potential (Yukawa potential) with the hard
wall potential as a confinement. It has been shown that the beginning of the crystallization of such a system is accompanied
by the formation of clusters with the hexagonal close packed (hcp) structure; a noticeable number of these clusters are then
transformed to the face centered cubic (fcc) phase. A plasma crystal formed after crystallization consists of the metastable
hcp phase, fcc clusters, and a small number of clusters with a body centered cubic (bcc) crystal lattice. Beginning with a
certain threshold value of the thermostat temperature, the number of fcc/bcc clusters decreases sharply with increasing temperature,
which is an important signature of the beginning of the melting of the plasma crystal. 相似文献
4.
5.
G. M. Petrov J. Davis 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(3):629-639
The dynamics of clusters irradiated by a high-intensity ultrashort pulse
laser has been studied using a fully relativistic three-dimensional
Molecular Dynamics Model. A fast three-dimensional tree algorithm for
computing the electrostatic force has been developed and compared with the
conventional particle-particle method. The particle-particle method requires
computation time, which scales as O(Np
2), and it is faster for small
number of particles Np <103. In the opposite case of relatively large
ensemble of particles Np >103, the preferred method is the tree
algorithm whose computation time scales as O(Np log Np). The tree
algorithm has been benchmarked against the particle-particle method for
clusters composed of xenon and deuterium atoms and its accuracy and
computation time have been analyzed. The optimum free parameter of the tree
method has been determined to be θ≈0.5. We addressed the
effects of boundary conditions by studying the contribution of adjacent
clusters to the total electromagnetic force exerted on individual particles.
We found that the adjacent clusters play a minor role in the overall cluster
dynamics. 相似文献
6.
P. M. Valov V. I. Leiman V. M. Maksimov O. Yu. Derkacheva 《Physics of the Solid State》2011,53(3):476-481
The kinetics of formation of CuCl nanoparticles in a glass has been studied. The experimental results obtained have been compared
with the results of calculations. A method has been developed for calculating the nucleation kinetics, which decreases the
time of calculations by a factor of several tens. This has been achieved using the joint kinetic equation for distributions
of clusters over the number of particles and over the radius. The distributions over the number of particles and over the
radius have been used for small and large clusters, respectively. The concentration of molecules near the surface of clusters
has been determined from the asymptotic solution of the diffusion equation. For subcritical clusters, the concentration of
molecules near the cluster surface has been taken to be equal to the average concentration in the solid solution. This method
has been used to calculate the nucleation kinetics of CuCl nanoparticles in a glass. The results obtained from the calculation
of the time dependences of the increase in the concentration and average radius of clusters agree well with experiment. 相似文献
7.
A new method based on the local analysis of the orientational order has been presented for analysis of the phase behavior of the Stockmayer fluid. A quantity has been introduced to quantitatively describe the ordering degree of particles at small distances. It has been used to analyze the phase diagram of the model under consideration. 相似文献
8.
The influence of the shape and size of nanocrystals on the lattice relaxation of body-centered cubic metals (zirconium, iron)
at a constant temperature has been investigated using the molecular dynamics method with the many-body interatomic interaction
potential obtained in terms of the embedded-atom model. The calculations have been performed for isolated clusters with sizes
ranging from 2.5 to 17 nm for zirconium and from 2 to 14 nm for iron. It has been demonstrated that, in free zirconium and
iron particles, the relaxation of the lattice constant along the [100], [010], and [001] directions has an oscillatory character.
Irrespective of the size of the zirconium and iron particles, the equilibrium distances between atoms at the center of cubic
clusters are minimum compared to those observed in near-surface layers and the equilibrium value of the lattice parameter
for the bulk sample. In spherical clusters, the region of a maximum contraction corresponds to a depth approximately equal
to 0.2 particle diameter from the surface. An increase in the size of both cubic and spherical clusters leads to a decrease
in the deviation of the local lattice parameter from the equilibrium value for the bulk sample. It has been established that
the size and shape of the cluster substantially affect the temperature and mechanism of the structural transformation from
the body-centered cubic phase into the hexagonal close-packed phase. 相似文献
9.
Finite clusters of atoms or molecules, typically composed of about 50 particles (and often as few as 13 or even less) have
proved to be useful prototypes of systems undergoing phase transitions. Analogues of the solid-liquid melting transition,
surface melting, structural phase transitions and the glass transition have been observed in cluster systems. The methods
of nonlinear dynamics can be applied to systems of this size, and these have helped elucidate the nature of the microscopic
dynamics, which, as a function of internal energy (or ‘temperature’) can be in a solidlike, liquidlike, or even gaseous state.
The Lyapunov exponents show a characteristic behaviour as a function of energy, and provide a reliable signature of the solid-liquid
melting phase transition. The behaviour of such indices at other phase transitions has only partially been explored. These
and related applications are reviewed in the present article. 相似文献
10.
Ferromagnetic and ferrimagnetic particles have been of scientific and technological interest for several decades. The study of nanometer clusters or particles is currently a developing subject. Such materials may be in a non-equilibrium or quasi-equilibrium phase; different properties as compared to the bulk and indeed even new physical phenomena may be expected. Some ways to synthesize clusters and fine particles are described. Mössbauer spectroscopy is shown to be particularly useful for the study of nanometer particles; an outline of how it actually works is given. As an illustration, barium ferrite small particles, a material of topical interest, is considered in detail. In particular, methods of preparation, the crystal and magnetic structure, the magnetic characteristics, recently obtained Mössbauer results, and potential and realized applications are reviewed. 相似文献
11.
利用紧束缚分子动力学方法研究了硅团簇Sin(n=5—10)的熔化行为.给出了团簇 熔化潜热 和熔点随团簇尺寸的变化关系,表明团簇熔化潜热和熔点强烈依赖于团簇的原子数.计算结 果表明硅团簇熔化机理与金属团簇熔化有很大不同,金属小团簇的熔化是一个从低温类固态 向高温类固态转变的过程,在转变温区,类固态和类液态处于动力学共存,而硅团簇在转变 温区则是处于一种中间态,这种中间态既不是类固态又不是类液态.比较了用不同计算方法 和定义方法所得硅团簇熔点.
关键词:
紧束缚
硅团簇
熔化潜热 相似文献
12.
The sputtering of clusters consisting of 13, 27, and 75 copper atoms from the (0001) graphite surface under bombardment by
Cu2 dimers with energies of 100, 200, and 400 eV has been simulated using the molecular dynamics method. A comparative analysis
of the distributions of backscattered particles and their energies over polar angles and the energy distributions of sputtered
atoms has been performed. The factors responsible for the large sputtering yield from surface clusters under their bombardment
with dimers as compared to copper and xenon monomers have been discussed. It has been demonstrated that, in the case of bombardment
with dimers, the substantial role in the sputtering of surface clusters is played by the overlap of collision cascades initiated
by each atom of the incident dimer. The differences in the sputtering under cluster and atom bombardments are especially pronounced
in the case of large surface clusters. 相似文献
13.
Jacob A. Friedman Metin Renksizbulut 《Particle & Particle Systems Characterization》1995,12(5):225-231
A method has been developed to increase the sensitivity of phase Doppler interferometry-based particle sizing systems to small particles in the presence of a spray containing large and small droplets; an important consideration when using seed particles to track the gas-phase velocity in multi-phase flows. The method, applicable to PDPA systems configured to operate in first and higher order refraction mode, involves doping the sprayed liquid with a dye that is strongly absorbing at the incident laser wavelengths. This results in greatly diminished scattered intensity from larger droplets, thus allowing the photomultiplier gain to be set to a level sufficient to easily detect small particles without saturation. Tests conducted indicate that, at a collection angle of 30° and droplet absorptivity of γ = 0.014/μm, the PDPA can accurately size absorbing droplets up to approximately 200 μm. This upper limit can be extended by changing selection angle. Tests performed with an actual spray demonstrated that the method allowed detection of 1 μm to 235 μm droplets; more than four times the instrument's usual range of 50: 1. A data correction scheme to determine the effective probe volume radius for each particle size class has been developed for absorbing particles, as standard correction schemes derived for non-absorbing droplets excessively weigh distributions toward smaller particles. 相似文献
14.
15.
K. G. Koss O. F. Petrov M. I. Myasnikov K. B. Statsenko M. M. Vasiliev 《Journal of Experimental and Theoretical Physics》2016,123(1):98-107
The results of experimental and numerical analysis are presented for phase transitions in strongly nonequilibrium small systems of strongly interacting Brownian particles. The dynamic entropy method is applied to analysis of the state of these systems. Experiments are carried out with kinetic heating of the structures of micron-size particles in a laboratory rf discharge plasma. Three phase states of these small systems are observed: crystalline, liquid, and transient. The mechanism of phase transitions in cluster structures of strongly interacting particles is described. 相似文献
16.
Roberto Livi Marco Pettini Stefano Ruffo Angelo Vulpiani 《Journal of statistical physics》1987,48(3-4):539-559
The relation between chaotic dynamics of nonlinear Hamiltonian systems and equilibrium statistical mechanics in its canonical ensemble formulation has been investigated for two different nonlinear Hamiltonian systems. We have compared time averages obtained by means of numerical simulations of molecular dynamics type with analytically computed ensemble averages. The numerical simulation of the dynamic counterpart of the canonical ensemble is obtained by considering the behavior of a small part of a given system, described by a microcanonical ensemble, in order to have fluctuations of the energy of the subsystem. The results for the Fermi-Pasta-Ulam model (i.e., a one-dimensional anharmonic solid) show a substantial agreement between time and ensemble averages independent of the degree of stochasticity of the dynamics. On the other hand, a very different behavior is observed for a chain of weakly coupled rotators, where linear exchange effects are absent. In the high-temperature limit (weak coupling) we have a strong disagreement between time and ensemble averages for the specific heat even if the dynamics is chaotic. This behavior is related to the presence of spatially localized chaos, which prevents the complete filling of the accessible phase space of the system. Localized chaos is detected by the distribution of all the characteristic Liapunov exponents. 相似文献
17.
Dynamics of the plume formation and parameters of the ejected clusters in short-pulse laser ablation 总被引:2,自引:0,他引:2
L.V. Zhigilei 《Applied Physics A: Materials Science & Processing》2003,76(3):339-350
The dynamics of the early stages of the ablation plume formation and the mechanisms of cluster ejection are investigated in
large-scale molecular dynamics simulations. The cluster composition of the ablation plume has a strong dependence on the irradiation
conditions and is defined by the interplay of a number of processes during the ablation plume evolution. At sufficiently high
laser fluences, the phase explosion of the overheated material leads to the formation of a foamy transient structure of interconnected
liquid regions that subsequently decomposes into a mixture of liquid droplets, gas-phase molecules, and small clusters. The
ejection of the largest droplets is attributed to the hydrodynamic motion in the vicinity of the melted surface, especially
active in the regime of stress confinement. Spatially resolved analysis of the dynamics of the plume formation reveals the
effect of segregation of the clusters of different sizes in the expanding plume. A relatively low density of small/medium
clusters is observed in the region adjacent to the surface, where large clusters are being formed. Medium-size clusters dominate
in the middle of the plume and only small clusters and monomers are observed near the front of the expanding plume. Despite
being ejected from deeper under the surface, the larger clusters in the plume have substantially higher internal temperatures
as compared to the smaller clusters. The cluster-size distributions can be relatively well described by a power law Y(N)∼N-τ with exponents different for small, up to ∼15 molecules, and large clusters. The decay is much slower in the high-mass region
of the distribution.
Received: 13 October 2001 / Accepted: 18 July 2002 / Published online: 25 October 2002
RID="*"
ID="*"Corresponding author. Fax: +1-434/982-5660, E-mail: lz2n@virginia.edu 相似文献
18.
The validity of the application of the dissipative particle dynamics (DPD) method to ferromagnetic colloidal dispersions has been investigated by conducting DPD simulations for a two–dimensional system. First, the interaction between dissipative and magnetic particles has been idealized as some model potentials, and DPD simulations have been carried out using such model potentials for a two magnetic particle system. In these simulations, attention has been focused on the collision time for the two particles approaching each other and touching from an initially separated position, and such collision time has been evaluated for various cases of mass and diameter of dissipative particles and model parameters, which are included in defining the equation of motion of dissipative particles. Next, a multi–particle system of magnetic particles has been treated, and particle aggregates have been evaluated, together with the pair correlation function along an applied magnetic field direction. Such characteristics of aggregate structures have been compared with the results of Monte Carlo and Brownian dynamics simulations in order to clarify the validity of the application of the DPD method to particle dispersion systems. The present simulation results have clearly shown that DPD simulations with the model interaction potential presented here give rise to physically reasonable aggregate structures under circumstances of strong magnetic particle–particle interactions as well as a strong external magnetic field, since these aggregate structures are in good agreement with those of Monte Carlo and Brownian dynamics simulations. 相似文献
19.
In the present work we introduce a simple, Nosé—Hoover style isothermal—isobaric molecular dynamics method for systems with holonomic molecular constraints and the molecular representation of the virial. We prove, using the non-Hamiltonian dynamics approach, recently developed by Tuckerman et al. [1999, Europhys. Lett., 45, 149], that the phase space distribution, generated by our equations, samples the desired ensemble under all circumstances. We also write down the explicit reversible integrator for our equations. This integrator has been implemented in the last version of the DLProtein program. 相似文献
20.
The dynamic and thermal properties of nanostructured materials based on aluminum with the periodic inclusions of Ti or Zr clusters have been investigated by the method of molecular dynamics. The elastic moduli, spectral vibrational densities of states, and temperature dependences of heat capacity for different Ti–Al and Zr–Al systems have been obtained. The effect of specific features of the phonon spectrum on the heat capacity of the nanocomposite lattice has been examined. It is shown that the ordering type and size of Ti/Zr clusters in the aluminum matrix significantly affect the elastic properties and heat capacity. The results obtained can be used for fabricating new aluminum-, titanium-, and zirconium-based composites with the desired properties. 相似文献