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1.
We present an extensive study of a new Monte Carlo acceleration algorithm introduced by Wolff for the Ising model. It differs from the Swendsen-Wang algorithm by growing and flipping single clusters at a random seed. In general, it is more efficient than Swendsen-Wang dynamics ford>2, giving zero critical slowing down in the upper critical dimension. Monte Carlo simulations give dynamical critical exponentsz
w=0.33±0.05 and 0.44+0.10 ind=2 and 3, respectively, and numbers consistent withz
w=0 ind=4 and mean-field theory. We present scaling arguments which indicate that the Wolff mechanism for decorrelation differs substantially from Swendsen-Wang despite the apparent similarities of the two methods. 相似文献
2.
In response to recent helium atom scattering (HAS) results, Monte Carlo (MC) simulations and perturbation theory have been performed for H2 on LiF(0 0 1). MC simulations predict that H2 molecules form a series of structures, p(2 × 2), p(8 × 2), p(4 × 2) with coverages Θ = 0.5, 0.625 and 0.75, respectively, that are stable up to 8 K. This is in partial agreement with the HAS results that report c(2 × 2) and c(8 × 2) structures; they agree in terms of coverage and stability, but disagree in terms of symmetry. To reconcile the results of the simulations and experiments, the orientation of the adsorbed H2 molecules was studied using perturbation theory. These calculations show that the adsorbed H2 molecules are azimuthally delocalized and that the structures are c-type rather then p-type. The calculations also indicate that p-H2 and helicoptering o-H2 prefer cationic sites, while cartwheeling o-H2 prefers anionic sites. 相似文献
3.
H. J. Herrmann 《Zeitschrift für Physik B Condensed Matter》1979,32(3):335-337
Analysis of Monte Carlo data shows the density profiles of critical percolation clusters (p=p
c
) to be similar to each other. The same is true for random animals (p=0). The exponents for these scaling laws are determined and agree with those expected from the cluster radii. 相似文献
4.
本文采用路径积分Monte Carlo (PIMC)方法研究仲氢团簇和正氘团簇的结构和超流体性质.比较仲氢团簇(分子数N≤40)在T=0.4 K,T=1.6 K的临近能量差和超流比例(superfluid fractions),发现仲氢团簇在T=0.4 K时出现"量子熔化"(quantum melting);研究了仲氢团簇的量子定域(quantum localization)和 "量子熔化"的关系,对T=0.4 K时仲氢及正氘团簇的量子定域与超流动性
关键词:
团簇
量子定域
量子熔化
超流比例 相似文献
5.
6.
Jack Alster 《Molecular physics》2013,111(6):1235-1239
The field gradient fluctuation at the Li+ nucleus in dilute aqueous solution is calculated via Monte Carlo simulations of Li+ + nH2O clusters (n = 6, 50 and 150). The intermolecular potentials and the lithium field gradient function, necessary for the simulations, are based on ab initio quantum mechanical calculations. It is found that the dominant contribution to the field gradient fluctuation at the lithium nucleus comes from the water molecules in the first shell. Furthermore, it is the lateral displacement of these molecules that causes the largest fluctuation. The contribution from the rotation of a water molecule is of minor importance. The field gradient at a lithium nucleus arising from a water molecule is badly described in a simple electrostatic model. 相似文献
7.
The processes of cluster formation in liquid alcohols, water, methanol, n-hexanol, and n-hexane have been investigated by the method of flicker-noise spectroscopy. Two types of clusters — clusters with a close-packed
structure and clusters with a loose structure — have been detected. The energy of formation of different clusters in methanol
and n-hexane ranges, respectively, from −250 to +250 J/mole and from −50 to +50 J/mole. The smallest clusters of methanol, n-hexanol, water, and n-hexane consist, respectively, of six, two, eleven, and two molecules, and their largest clusters represent oscillators consisting,
respectively, of 50,400, 17,200, 93,500, and 33,150 molecules at 274 K. In methanol at 271 K, more than 44 types of clusters
consisting of 6, 97, 152, 219, 297, 492, 1029, 1368, 1560, etc. molecules were detected. In n-hexanol at 273 K, 57 types of clusters were detected. Models of small clusters are proposed. In water, the content of close-packed
clusters is maximum at 277 K. The energy of formation/decomposition of small clusters in water ranges from −0.4 to +0.4 kJ/mole
and increases with increase in the water temperature. The hysteresis of transformation of the (H2O)280 cluster in the process of heating and cooling of water in the temperature range 273–280 K was detected. Series of energy
spectra of clusters in liquids at different temperatures are presented and discussed.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 305–312, May–June, 2005. 相似文献
8.
P. Bandyopadhyay A. K. Ojha T. K. Barik A. Roy 《Journal of Raman spectroscopy : JRS》2008,39(7):827-831
Raman measurements on Gillette foam have been carried out to analyze different phases of water in the system. We have shown that in addition to free water molecules, which drain out with aging of foam, water clusters of only a few water molecules are also present in foam. We have analyzed the rate of drainage with the existing theory available in the literature. The nature of water clusters in Gillette foam has also been obtained from ab initio self‐consistent field calculations for [H2O]n clusters. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
9.
M.-H. Du L.-L. Wang A. Kolchin H.-P. Cheng 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):323-326
The interaction of water with SiO
2 is an important problem in geophysics,
materials physics, and environmental science. In this paper, we
present recent results on studies of H
2
O-silica clusters from first-principles
Born-Oppenheimer molecular dynamics calculations. Bond strength
and chemical stability are investigated as a function of cluster
size and chemical composition. Both physisorption and
chemisorption of water molecules on the clusters are discussed
via analysis of energetics.
Calculations of clusters are compared with the results from
extended surfaces. The validity of clusters as models of
surfaces is discussed. 相似文献
10.
M.A. Gaveau M. Briant P.R. Fournier J.M. Mestdagh J.P. Visticot F. Calvo S. Baudrand F. Spiegelman 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(2):153-161
Spectroscopic experiments have been performed, providing emission and excitation spectra of calcium atoms trapped on argon
clusters of average size 2 000. The two experimental spectra fall in the vicinity of the calcium resonance line 1P 1 → 1S0 at 422.9 nm. The excitation spectrum consists in two bands located on each side of the resonance line of the free calcium.
In addition, Monte Carlo calculations, coupled to Diatomics-In-Molecule potentials are employed to simulate the absorption
spectrum of a single calcium atom in the environment of a large argon cluster of average size 300. The theoretical absorption
spectrum confirms the existence of two bands, and shows that these bands are characteristic of a calcium atom located at the
surface of the argon cluster and correspond to the excited 4p orbital of calcium either perpendicular or parallel to the cluster surface. The precise comparison between the shape of the
absorption spectrum and that of the fluorescence excitation spectrum shows different intensity ratios. This could suggest
the existence of a non adiabatic energy transfer that quenches partly the fluorescence of trapped calcium. Another explanation,
although less likely, could be a substantial dependence of the calcium oscillator strength according to the alignment of the
calcium excited orbital with respect to the cluster surface. The emission spectrum always shows a band in the red of the resonance
line which is assigned to the emission of calcium remaining trapped on the cluster. When exciting the blue band of the excitation
spectrum, the emission spectrum shows a second, weak, component that is assigned to calcium atoms ejected from the argon clusters,
indicating a competition between ejection and solvation.
Received 7 May 2002 Published online 1st October 2002
RID="a"
ID="a"e-mail: jmm@drecam.saclay.cea.fr
RID="b"
ID="b"URA 2453 du CNRS
RID="c"
ID="c"UMR 5626 du CNRS 相似文献
11.
The low-temperature plasticity of solid polycrystalline parahydrogen doped with an isotopic impurity (deuterium) is studied. The dependences of the rate of steady-state creep in p-H2 on the impurity concentration and stress are obtained. The deformation of p-H2 is described with inclusion of the zero-point mean-square displacements 〈x2〉 of particles making up a crystal. The calculated and experimental values of 〈x2〉 are compared for two possible isotope molecules (HD and D2) at three stress levels. A correlation between the 〈x2〉 values and an increase in the force constants of a p-H2 crystal doped with the isotopic impurity is established. An increase in the mean-square displacements of p-H2 with the tensile load is discussed. Deformation-induced purification of a p-H2 crystal from the isotopic impurity is suggested to occur. 相似文献
12.
A. V. Khakhalin A. V. Koroleva V. T. Shalabaeva Ya. N. Shirshov 《Moscow University Physics Bulletin》2012,67(4):364-371
Computer simulation of water clusters (H2O) n , Na+(H2O) n and K+(H2O) n (n ?? 8) at temperatures of 1 and 300 K was carried out using the Monte Carlo method. All the types of the hydrogen-bond network structures at equilibrium configurations of the water clusters and, among them, the most probable ones at temperatures of 1 and 300 K, were detected. The analysis of the most probable types of hydrogen-bond networks at equilibrium configurations of water clusters revealed that clusters with n water molecules inherit the configuration of clusters with n ? 1 water molecules with an accuracy of one hydrogen bond. 相似文献
13.
Victor Pereyra Peter Nielaba Kurt Binder 《Zeitschrift für Physik B Condensed Matter》1995,97(2):179-187
A qualitative model for solid mixtures of diatomic molecules, where one species (called CO, to be specific) carries both a dipole moment and a quadrupole moment, while the other species (calledN
2) has only a quadrupole moment, is studied by Monte Carlo methods. We use spinsS
i
=±1 to represent the orientations of the CO electric dipole moment, if the lattice sitei is taken by a CO molecule, whileS
i
=0 if the site is taken by anN
2 molecule. Assuming nearest-neighbor antiferroelectric interactions between CO molecules, and a bilinear dipole-quadrupole coupling between CO andN
2, the randomly quenchedN
2 molecules act like random fields do in the random field Ising model. In previous work it was already shown that this crude model is in very good agreement with experimental data in two dimensions (adsorbed layers), where the random fields induces a rounding of the transition. Here Monte Carlo simulations of the three-dimensional version of this model are presented and analyzed with finite size scaling concepts. As expected from the theory, a behaviour qualitatively different from the two-dimensional case is detected. The Monte Carlo data provide qualitative evidence that the random field induces crossover to an universality class with critical exponents distinct from the pure Ising model, but it is not feasible to us to study large enough systems that would allow a reliable estimation of these exponents. But the results show that dilution without dipole-quadrupole coupling has much less drastic effects on the critical behavior, and that in the presence of this coupling very small impurity concentrations do indeed change the critical behavior.This paper is dedicated to Professor Herbert Wagner on the occasion of his 60th birthday 相似文献
14.
Kurt Kremer 《Zeitschrift für Physik B Condensed Matter》1981,45(2):149-152
A Monte Carlo study of SAW's on a diluted diamond lattice is presented. We find that the exponentv does not change by dilution,v0.59 as in the undiluted case, in contrast to the original conclusion of Chakrabarti and Kertész. This result cannot be understood by the Harris criterion. At the percolation concentrationp
c
of the lattice we find a higher exponentv
pc
2/3. A scaling form of the crossover between these exponents nearp
c
is proposed and found to be consistent with the Monte Carlo results. 相似文献
15.
采用密度泛函理论(density functional theory, DFT) 在B3LYP/LANL2DZ基组水平上对钨团簇吸附CO分子进行了系统研究. 结果表明, WnCO团簇的基态结构是在Wn团簇中性或阴离子基态结构的基础上吸附CO生长而成; CO的吸附以端位吸附为主,桥位吸附为辅; CO分子在Wn团簇表面发生的是非解离性吸附. 与优化的CO键长(0.116 nm)相比,吸附后C-O键长变长(0.120–0.123 nm), 表明吸附后C-O键被削弱, CO分子被活化了.稳定性分析表明,在所研究的团簇中, W3CO和W5CO团簇的稳定性较强;自然键轨道(NBO)分析表明, W原子与CO分子相互作用的本质是CO分子内的杂化轨道与W原子6s, 5d, 6p和6d轨道相互作用的结果.
关键词:
nCO (n= 1–6)团簇')" href="#">WnCO (n= 1–6)团簇
基态构型
稳定性
电子性质 相似文献
16.
The parting limit or de-alloying threshold for electrolytic dissolution of the more reactive component from a homogeneous fcc binary alloy is usually between 50 and 60 at%. The system that has been most studied, dissolution of Ag from Ag–Au, shows a parting limit close to 55 at% Ag. Here, Kinetic Monte Carlo (KMC) simulations of ‘Ag–Au’ alloys and geometric percolation modeling are used to study the relationship between this parting limit and the high-density site percolation thresholds p c(m) for an fcc lattice, subject to the rule that atoms with coordination greater than nine are prevented from dissolution. The value of p c(9) is calculated from geometric considerations to be 59.97 ± 0.03%. In comparison, using KMC simulations with no surface diffusion and no dissolution allowed for ‘Ag’ atoms with more than nine total neighbors, the parting limit is found to be slightly lower (58.4 ± 0.1%). This slight discrepancy is explained by consideration of the local atomic configurations of ‘Ag’ atoms – a few of these configurations satisfy the percolation requirement but do not sustain de-alloying, while a larger number show the converse behavior. There is still, however, an underlying relationship between the parting limit and the percolation threshold, because being at p c(9) guarantees a percolation path in which successive ‘Ag’ atoms share at least one other ‘Ag’ neighbor. With realistic kinetics of surface diffusion for ‘Au’, the parting limit drops to 54.7 ± 0.3% because a few otherwise inaccessible dissolution paths are opened up by surface diffusion of ‘Au’. 相似文献
17.
Monte Carlo simulations show that, at one monolayer coverage, H2 molecules adsorbed on a NaCl(0 0 1) surface occupy all Na+ sites and form a commensurate c(2 × 2) structure. If the Cl− sites are occupied as well, a bi-layer p(2 × 1) structure forms. An examination of the H2 molecules’ rotational motion shows the molecular axes are azimuthally delocalized and so both of the structures acquire (1 × 1) symmetry in accord with experimental observations. These calculations also show that helicoptering o-H2 (J = 1, m = ±1) prefer to sit on top of Na+ sites, while cartwheeling o-H2 (J = 1, m = 0) prefers to locate over Cl− sites, in agreement with other work. 相似文献
18.
Systematic study of small BN clusters 总被引:2,自引:0,他引:2
S. Guerini P. Piquini 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):17-20
We performed a systematic investigation of the small BxNy (x + y? 6) clusters using the ab initio Hartree-Fock scheme plus second-order perturbation theory. The nature of the potential energy surface extrema are analyzed
through analytical total energy second derivatives. Ionization potentials, binding energies and the stability against some
possible reaction mechanisms are calculated. Based on these results we propose that the growing process for these clusters
is mainly due to the successive incorporation of BN molecules. A discussion of some mass spectrometry experimental results
is also presented.
Received 2 October 2000 相似文献
19.
F. Calvo F. Spiegelman M. A. Gaveau M. Briant P. R. Fournier J. M. Mestdagh J. P. Visticot 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):215-218
The finite temperature optical spectroscopy of
CaArn clusters in the range
6
n
146
is investigated using a Diatomics-In-Molecule (DIM) Hamiltonian
and classical parallel tempering Monte Carlo simulations. The
absorption spectrum is calculated in the vertical approximation
at various temperatures between 2 K and 50 K. Several typical
situations are reported. CaAr6 shows a
strong thermal broadening and shift of the spectral lines,
possibly associated with isomerization.
CaAr13 only shows some broadening.
CaAr37 exhibits features corresponding to
coexisting isomers at low temperature. Finally, the abrupt
changes in the absorption spectrum in
CaAr146 at about 20 K are indicative of
surface diffusion. 相似文献