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1.
N.T. Wilson R.L. Johnston 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(1):161-169
Molecular Dynamics Simulated Annealing has been used to probe the structure of small Au clusters consisting of between 2 and
40 atoms. The interatomic interactions within these clusters are described using an empirical Murrell-Mottram many-body potential
energy function. Four distinct structural motifs are present in the structures of the predicted global minima, based on octahedra,
decahedra, icosahedra and hexagonal prisms.
Received 30 September 1999 and Received in final form 23 March 2000 相似文献
2.
F.A. Gianturco F. Sebastianelli 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,10(3):399-414
The structural properties of some of the smaller ionic clusters of neon atoms are examined at the post-Hartree-Fock level
using a variety of correlation corrections described within a Density Functional treatment. The results of the calculations,
and the physical reliability of the method, are discussed in comparison with earlier theoretical results and with the scanty
experimental data. The possible presence of a dimeric ion as the core ionic moiety of all the clusters is indicated by the
present treatment which also underlines the weaker binding of the outer “shells” of Ne atoms to the central moiety and the
rather marked overall charge localization into the central ionic core of the clusters.
Received 30 December 1999 and Received in final form 29 February 2000 相似文献
3.
J. Akola A. Rytkönen H. Häkkinen M. Manninen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(1):93-99
The ionization potential of sodium clusters () at a finite temperature is studied using density functional theory and ab initio molecular dynamics. The threshold regions of the photoionization efficiency curves are deduced from the integrated IP distributions,
which are obtained from the energy eigenvalues of the highest occupied Kohn-Sham states during molecular dynamics by applying
a theoretically well-defined shift. The calculated ionization potentials are directly compared to the experimental values.
The energetically best geometry of Na55 is found to be a slightly distorted icosahedron.
Received 16 April 1999 and Received in final form 6 July 1999 相似文献
4.
C. Coudray G. Blaise M.J. Malliavin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(1):127-136
With the help of ab initio methods the clusters [(MgO)13Mg]
Q+
are simulated for Q = 0, 1, 2. Then, vacancy clusters [(MgO)12Mg2]
Q+
obtained by removing one oxygen atom are computed for Q running from 0 to 4. These clusters exhibit a slight sphericity and generally shorter interatomic distances than in the crystal.
The electronic densities variations are studied in function of Q. In particular, it is observed that the electronic density in the oxygen vacancy goes to a maximum when Q = 2. The ionisation potentials vary from approximately 4 to 14 eV when Q varies from 0 to 3, with a more rapid increase from Q = 1 to Q = 2. The stability study of vacancy clusters show that they experience a phase transition when their charge becomes equal
to 2, in accordance with the features mentioned above.
Received 14 September 1999 and Received in final form 2 December 1999 相似文献
5.
The internal energy of small ammonia clusters in a supersonic beam and after scattering off LiF(100)
C. Menzel H. Zacharias 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(1):109-114
The photoionization efficiency (PIE) of neutral ammonia clusters is studied as a function of photon energy. From these curves
the internal energies of clusters in the incident supersonic beam and of clusters surviving after scattering off a LiF(100)
surface are derived. A supersonic expansion of ammonia seeded in He produces small clusters of various size but with uniform
kinetic energy of about 285 meV per monomer molecule. The mass distribution of clusters in the jet and of the scattered particles
is measured in a reflecting time-of-flight mass spectrometer by single photon photoionization using vacuum ultraviolet (VUV)
laser radiation tunable between
and
. In the incident beam the internal energies of clusters up to n = 15 do not vary significantly and amount to an average of about . After scattering off LiF(100) the internal energy of clusters up to n = 4 increases with fragment size and amounts to about half a monomer binding energy.
Received 18 October 1999 and Received in final form 10 December 1999 相似文献
6.
A. Balerna L. Liotta A. Longo A. Martorana C. Meneghini S. Mobilio G. Pipitone 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,6(1):89-97
Silver-palladium bimetallic clusters were synthesized on pumice by the reduction of aqueous solution of metal salts with different
Pd:Ag ratios. Used as bimetallic catalysts, in hydrogenation reactions, in situations where molecules can undergo several
different reactions, they eliminate undesired reactions and maximize the desired ones. To characterize the structure of these
bimetallic catalysts and control if the two metallic elements do mix or not to each other to form an alloy, the structure
of the Ag-Pd bimetallic clusters was investigated by means of X-ray-absorption fine-structure spectroscopy (XAFS) and anomalous
wide angle X-ray scattering (AWAXS) experiments performed at the European Synchrotron Radiation Facility (ESRF) using the
GILDA and the BM16 beamlines. A correlation between Ag and Pd was found but not a clear evidence of alloying.
Received: 21 December 1998 / Received in final form: 19 March 1999 相似文献
7.
R. Popescu D. Macovei A. Devenyi R. Manaila P.B. Barna A. Kovacs J.L. Lábár 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(4):737-743
Structure of metal clusters and of the C60 matrix in Au/C60 and Cu/C60 nanosystems was investigated by X-ray diffraction. Results support a charge-transfer-type interaction at the metal-C60 interface, which affects the size distribution of metal clusters, favouring interstitial location of metal ions in the fullerite
lattice.
Received 5 February 1999 and Received in final form 7 July 1999 相似文献
8.
C. Nützenadel A. Züttel D. Chartouni G. Schmid L. Schlapbach 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(2):245-250
Metal hydrides are used for electrochemical or gaseous storage of hydrogen because considerable amounts of hydrogen are reversibly
absorbed and desorbed at interstitial sites. Palladium is often used as a model system. Nanophase material is of interest
because properties related to the hydrogen absorption are size dependent. In this study, clusters from the size of 55 to 1415
atoms are investigated and compared with bulk Pd. It turns out that not only the amount of hydrogen per palladium that can
be intercalated changes but also kinetics and chemical potentials are dependent on the cluster size. The clusters used for
this study were chemically synthesised and stabilised by a ligand shell.
Received 9 October 1998 and Received in final form 10 May 1999 相似文献
9.
C. Yannouleas U. Landman A. Herlert L. Schweikhard 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):81-85
Using Penning-trap experiments and a shell-correction method incorporating ellipsoidal shape deformations, we investigate
the formation and stability patterns of trianionic gold clusters. Theory and experiment are in remarkable agreement concerning
appearance sizes and electronic shell effects. In contrast to multiply cationic clusters, decay of the trianionic gold clusters
occurs primarily via electron autodetachment and tunneling through a Coulomb barrier, rather than via fission.
Received 9 January 2001 相似文献
10.
M. Bertolus V. Brenner P. Millié 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,1(2):197-205
A theoretical study of clusters with using density functional theory is presented. Tests of various functionals demonstrate that local spin density approximation
(LSDA) is the most adequate functional for the study of these systems. Structures, vibrational frequencies, and IR intensities
of the lowest energy isomer of the studied clusters obtained using LSDA are described, and the unusual properties of the Si-C
clusters are discussed. A quantitative analysis of the obtained structures was carried out, and relations between the coordinations,
interatomic distances, and angles observed in the Si-C clusters were obtained through introduction of the notion of coordination.
This analysis also shows that the carbon atoms mainly exhibit sp and sp2 hybridizations, and that a majority of silicon atoms do not hybridize. This study is the fi
rst step of the implementation of a semi-empirical potential, which would describe the moderately small Si-C clusters.
Received: 20 October 1997 / Received in final form: 16 December 1997 / Accepted: 17 December 1997 相似文献
11.
M. Bertolus V. Brenner P. Millié 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(3):387-394
An ab initio study of the Nan(OH)n, Nan(OH)n-1
+, Agn(OH)n, and Agn(OH)n-1
+ clusters with n up to four is presented. The results of this study show that, in accordance with experimental observations, the sodium hydroxide
clusters are almost purely ionic, while the Ag-O bond exhibits a significant covalent character. The perturbation caused by
the non-spherical OH- group relatively to an atomic anion, as well as the influence on structures and energies of the covalent character of the
metal-oxygen bond are determined. The appearance of metal-metal bonds in the silver hydroxide clusters is also discussed.
Finally, the theoretical results obtained on the Na-OH clusters are compared to experimental results available on the dissociation
of the Nan(OH)n-1
+ clusters.
Received 9 August 1999 and Received in final form 1st December 1999 相似文献
12.
J.M. Weber I.I. Fabrikant E. Leber M.-W. Ruf H. Hotop 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(2):247-256
Using laser photoelectron attachment to methyl iodide clusters in a differentially-pumped seeded supersonic helium beam and
mass spectrometric ion detection, we have measured the rate coefficients for formation of (q = 0-2) ions over the electron energy range 0-100 meV with an effective energy width of about 2.5 meV. Whereas a prominent
vibrational Feshbach resonance just below the onset for the C-I stretch vibration ( ) is observed for dissociative attachment to monomers (yielding I- ions), only weak and broad structure, shifted to lower energies, is detected for formation of ions and essentially no structure is left in the attachment spectrum for . These observations are interpreted by model R-matrix calculations which successfully describe the DA cross-section for the monomer and qualitatively recover the trend
observed for cluster ion formation. For the clusters, the effects of increased electron-target long-range interaction and
of solvation as well as coupling to soft vibrational modes lead to strong broadening and shifting of the vibrational Feshbach
resonance and, ultimately, to its disappearance.
Received 29 November 1999 and Received in final form 14 January 2000 相似文献
13.
V. N. Kondratyev Ph. Blanchard H. O. Lutz 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(2):241-244
The multi-fragmentation dynamics of noble gas atomic clusters is considered for different statistically distributed deposited
energies. The conditions giving rise to the development of criticality in the cluster evolution are revealed from an analysis
of the signals in the fragment mass distribution. The time dependence of the observables related to critical exponents is
studied. It is demonstrated that in a certain regime the cluster exhibits a behavior which can be identified as the precursor
of a second-order liquid-gas phase transition.
Received 1st September 1998 and Received in final form 14 January 1999 相似文献
14.
S. Kümmel T. Berkus P.-G. Reinhard M. Brack 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(2):239-245
The static electric dipole polarizability of Na
N
clusters with even N has been calculated in a collective, axially averaged and a three-dimensional, finite-field approach for , including the ionic structure of the clusters. The validity of a collective model for the static response of small systems
is demonstrated. Our density functional calculations verify the trends and fine structure seen in a recent experiment. A pseudopotential
that reproduces the experimental bulk bond length and atomic energy levels leads to a substantial increase in the calculated
polarizabilities, in better agreement with experiment. We relate remaining differences in the magnitude of the theoretical
and experimental polarizabilities to the finite temperature present in the experiments.
Received 8 November 1999 相似文献
15.
S.A. Prosandeev V.S. Vikhnin S. Kapphan 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):469-474
Experimental data on the temperature and electric field dependence of the Second Harmonic Generation Intensity in the solid
solution KTaO3:Li is analyzed in the framework of a new percolation-type approach which considers the history of cluster formation averaged
over a large number of samples. In order to take into account that two cluster dipole moments turn when joining clusters together,
a constraint is imposed on the cluster growth. This constraint leads to cluster-size saturation just after the percolation
threshold. Owing to this circumstance, the connected cluster coexists with free clusters in some range of the impurity concentration
and temperature. There is qualitative agreement between the computational results and experiments on Second Harmonic Generation
intensities. The algorithm was written in C++ which allowed realistic computations to be performed on a standard PC.
Received 26 August 1999 and Received in final form 27 December 1999 相似文献
16.
P.A. Marcos J.A. Alonso A. Rubio M.J. López 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,6(2):221-233
The thermal stability, phases and phase changes of small carbon clusters and fullerenes are investigated by constant energy
Molecular Dynamics simulations performed over a wide range of temperatures, i.e., from to above the melting point of graphitic carbon. The covalent bonds between the carbon atoms in the clusters are represented
by the many-body Tersoff potential. The zero temperature structural characteristics of the clusters, i.e., the minimum energy structures as well as the isomer hierarchy can be rationalized in terms of the interplay between the
strain energy (due to the surface curvature) and the number of dangling bonds in the cluster. Minimization of the strain energy
opposes the formation of cage structures whereas minimization of the number of dangling bonds favors it. To obtain a reliable
picture of the processes experienced by carbon clusters as a function of temperature, both thermal and dynamical characteristics
of the clusters are carefully analyzed. We find that higher excitation temperatures are required for producing structural
transformations in the minimum energy structures than in higher lying isomers. We have also been able to unambiguously identify
some structural changes of the clusters occurring at temperatures well below the melting-like transition. On the other hand,
the melting-like transition is interrupted before completion, i.e., the thermal decomposition of the clusters (evaporation or ejection of or units) occurs, from highly excited configurations, before the clusters have fully developed a liquid-like phase. Comparison
with experiments on the thermal decomposition of and a discussion of the possible implications of our results on the growth mechanisms leading to the formation of different
carbon structures are included.
Received: 25 March 1998 / Received in final form: 30 October 1998 相似文献
17.
O. Diéguez R.C. Longo C. Rey L.J. Gallego 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(4):573-576
Using the noncentral embedded atom model potential recently proposed by Besson and Morillo for bulk alloys (), we performed computer simulations to predict the ground-state configurations of and clusters (). The computed structures of clusters are in general agreement with such theoretical results as have been obtained by density functional calculations
(i.e. for ). The results for Fe-rich clusters show surface segregation of Al, which is in keeping with the findings of a previous study of clusters.
Received 29 April 1999 相似文献
18.
F. Duque L.M. Molina M.J. López A. Ma nanes J.A. Alonso 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):285-288
The electronic and atomic structure of Al13H has been studied using Density Functional Theory. Al13H has closed electronic shells. This makes the cluster very stable and suggests that it could be a candidate to form cluster
assembled solids. The interaction between two Al13H clusters was analyzed and we found that the two units preserve their identities in the dimer. A cubic-like solid phase assembled
from Al13H units was then modeled. In that solid the clusters retain much of their identity. Molecular dynamics runs show that the
structure of the assembled solid is stable at least up to 150 K. A favorable relative orientation of the clusters with respect
to their neighbors is critical for the stability of that solid.
Received 21 November 2000 相似文献
19.
Ajeeta Dhavale D.G. Kanhere C. Majumder G.P. Das 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,6(4):495-500
The ground-state geometries, energetics and the stability of
(
n
=1-12) clusters are studied using ab initio molecular dynamics method. Our results indicate that the ground-state geometries of large clusters () are different from those of clusters where a trivalent impurity Al is added to the same monovalent host Na. Other features observed are an early appearance
of 3-dimensional structure and a pentagonal growth path from n
=6 up to n
=11. As expected, the ground-state geometry of is not an icosahedron but can be viewed as a distorted form of one of the low lying geometries of cluster. In the energetically favored structures impurity atom Mg is never located at the center of the cluster. The stability
analysis based on the energetics shows (8 valence electrons) to be the most stable. In addition there is a remarkable even-odd pattern observed in the dissociation
energy and the second difference in energy which is absent in earlier studies of and clusters.
Received: 16 September 1998 / Received in final form: 15 February 1999 相似文献
20.
J. Lermé B. Palpant B. Prével E. Cottancin M. Pellarin M. Treilleux J.L. Vialle A. Perez M. Broyer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(1):95-108
The optical response of free and matrix-embedded gold metal clusters AuN is investigated in the framework of the time-dependent local-density-approximation (TDLDA). The characteristics of the surface
plasmon resonance are carefully analyzed as a function of the model parameters and the particle radius. The strong influence
of the frequency-dependence of the 5d core-electron dielectric function in the vicinity of the interband threshold is emphasized. The size evolution of the Mie-frequency
in free gold clusters exhibits a noticeable blue-shift trend as the particle size decreases, much stronger than in silver
clusters. The width and shape of the resonance, essentially ruled by the decay via the interband transitions, are found closely correlated to the imaginary component of the core-electron dielectric function.
In presence of a surrounding matrix the blue-shift trend is largely rubbed out. Agreement with recent experimental results
on size-selected gold clusters embedded in an alumina matrix may be achieved by taking into account the porosity effects at
the metal/matrix interface. The comparison with the predictions of classical models is also provided.
Received: 9 March 1998 / Revised: 5 June 1998 / Accepted: 3 July 1998 相似文献