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1.
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
2.
M.A. Lebeault J. Viallon J. Chevaleyre C. Ellert D. Normand M. Schmidt O. Sublemontier C. Guet B. Huber 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):233-242
We exposed small size-controlled lead clusters with a few hundreds of atoms to laser pulses with peak intensities up to 1015 W cm-2 and durations between 60 fs to 2.5 ps. We measured kinetic energies and ionic charge of fragments as a function of the laser
intensity and pulse duration. Highly charged Pbn+ ions up to n = 26 have been detected presenting kinetic energies up to 15 keV. For comparison with our experimental results, we have performed
simulations of the laser coupling with a cluster-sized lead nanoplasma using a qualitative model that was initially proposed
by Ditmire and co-workers at LLNL for the case of rare gas clusters. From these simulations we conclude that two mechanisms
are responsible for the explosion dynamics of small lead clusters. As already observed for large rare gas clusters (n = 106), fragments with charge states below +10 are driven by Coulomb forces, whereas the higher charged fragments are accelerated
by hydrodynamic forces. The latter mechanism is a direct consequence of the strong laser heating of the electron cloud in
the nanoplasma arising from a plasmon-like resonance occurring at n
e = 3n
c. In order to obtain an optimized laser-nanoplasma coupling, our results suggest that the plasma resonance should occur at
the peak intensity of the laser pulse. Due to inertial effects, even for such small-sized clusters, the observed optimum pulse
duration is in the order of 1 ps which is in good agreement with our theoretical results.
Received 18 March 2002 Published online 19 July 2002 相似文献
3.
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
4.
V. Kumar 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):227-232
We report the recent findings of metal (M) encapsulated
clusters of silicon from computer experiments based on
ab initio total energy
calculations and a cage shrinkage and atom removal approach. Our
results show that using a guest atom, it is possible to wrap
silicon in fullerenelike (f)
structures, as sp2 bonding is not
favorable to produce empty cages unlike for carbon. Transition M
atoms have a strong bonding with the silicon cage that are
responsible for the compact structures. The size and structure
of the cage change from 14 to 20 Si atoms depending upon the
size and valence of the M atom. Fewer Si atoms lead to
relatively open structures. We find cubic,
f, Frank-Kasper (FK)
polyheral type, decahedral, icosahedral and hexagonal structures
for M@Sin with n = 12-16 and several different M
atoms. The magic behavior of 15 and 16 atom Si cages is in
agreement with experiments. The FK polyhedral cluster,
M@Si16 has an exceptionally large density
functional gap of about 2.35 eV calculated within the
generalized gradient approximation. It is likely to give rise to
visible luminescence in these clusters. The cluster-cluster
interaction is weak that makes such clusters attractive for
cluster assembled materials. Further studies to stabilize
Si20 cage with M = Zr, Ba, Sr, and Pb
show that in all cases there is a distortion of the
f cage. Similar studies on M
encapsulated germanium clusters show FK polyhedral and
decahedral isomers to be more favorable. Also perfect
icosahedral M@Ge12 and
M@Sn12 clusters have been obtained with
large gaps by doping with divalent M atoms. Recent results of
the H interaction with these clusters, hydrogenated silicon
fullerenes as well as assemblies of clusters such as nanowires
and nanotubes are briefly presented. 相似文献
5.
K. Ohshimo H. Tsunoyama F. Misaizu K. Ohno 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):107-110
Intracluster electron transfer and oligomerization reaction were investigated by mass spectrometry of clusters of alkali metal
atom (M) with acrylonitrile (AN; CH2=CHCN). In the photoionization mass spectra of M(AN)n, magic numbers were clearly observed at n = 3k (k = 1-4 for M = Na and K, k = 1 for M = Li). The results of photodissociation of neutral K(AN)n indicate that the n = 3 cluster has an anomalous stability relative to other sizes of clusters. The C=C bond in vinyl molecules is also found
to be necessary to form the magic numbers by measuring the photoionization mass spectrum of K atom with propionitrile. These
results strongly support the intracluster anionic oligomerization reaction initiated by electron transfer from the alkali
atom. The quantum chemical calculations have revealed that the evaporation induced by excess energy generated by intracluster
oligomerization is important to form the magic numbers in the present clusters.
Received 29 November 2000 相似文献
6.
E. Kasabova D. Alamanova M. Springborg V. G. Grigoryan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):425-431
The soft deposition of Ni13 and Cu13 clusters on Ni(111) and Cu(111) surfaces is studied by
means of constant-energy molecular-dynamics simulations.
The atomic interactions are described by the Embedded Atom Method.
It is shown that the shape of the nickel clusters deposited on Cu(111) surfaces remains rather intact,
while the copper clusters impacting on Ni(111) surfaces collapse forming double and triple layered
products. Furthermore, it is found that for an impact energy of 0.5 eV/atom the structures of all
investigated clusters show the lowest similarity to the original structures, except for the case of
nickel clusters deposited on a Cu(111) surface. Finally, it is demonstrated that when cluster and
substrate are of different materials, it is possible to control whether the deposition results in
largely intact clusters on the substrate or in a spreading of the clusters. This separation into
hard and soft clusters can be related to the relative cohesive energy of the crystalline materials. 相似文献
7.
J. Zhao Y. Luo G. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(3):309-316
Tight-binding model is developed to study the structural and electronic properties of silver clusters. The ground state structures
of Ag clusters up to 21 atoms are optimized by molecular dynamics-based genetic algorithm. The results on small Agn clusters (n = 3-9) are comparable to ab initio calculations. The size dependence of electronic properties such as density of states, s-d band separation, HOMO-LUMO gap, and ionization potentials are discussed. Magic number behavior at Ag2, Ag8, Ag14, Ag18, Ag20 is obtained, in agreement with the prediction of electronic ellipsoid shell model. We suggest that both the electronic and
geometrical effect play significant role in the coinage metal clusters.
Received 7 August 2000 相似文献
8.
We have experimentally studied the dissociation/coalescence of internal Plateau borders (PBs) in simple monolayer bubble clusters, as a result of changing the liquid fraction. At large liquid content, the clusters consist of n bubbles of the same size, symmetrically placed around an internal n-sided PB (n-PB). On decreasing the liquid fraction we observed symmetry-breaking transitions in the 4- and 5-bubble clusters (but not in the 3-bubble cluster), followed by dissociation of the PBs. We used the Surface Evolver to determine the various equilibrium configurations of the corresponding two-dimensional wet clusters and their surface energies. The sequence of 4-bubble cluster configurations observed on varying the liquid fraction correlates qualitatively with that predicted on the basis of Surface Evolver calculations. The same is not true of the 5-bubble cluster. 相似文献
9.
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
10.
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
11.
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
12.
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
13.
G. E. Ntamack F. Chandezon B. Manil H. Lebius S. Tomita C. Guet M. G. Kwato Njock B. A. Huber 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):153-156
Highly charged sodium clusters produced in collisions
between neutral clusters and multiply charged ions are formed
within a large range of temperatures and fissilities, and
identified by means of a high-resolution reflectron-type
time-of-flight mass spectrometer ( m/m
14000). The limit of stability of these charged clusters is
experimentally investigated, and the time-of-flight spectra are
compared with theoretical spectra based on Monte-Carlo
simulations. The results indicate that the maximum fissility
(X) of stable clusters is
approaching the Rayleigh limit (X = 1) for larger clusters sizes. It is
mainly limited by the initial neutral cluster temperature (
T 100 K) and the energy
transfer in the ionizing collision. In addition, the comparison
between the measured and simulated spectra suggests for high
cluster charges a multi-fragmentation process, in which most of
charge is emitted, creating low charged residual cluster ions. 相似文献
14.
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
15.
Fortes MA Rosa ME Vaz MF Teixeira PI 《The European physical journal. E, Soft matter》2004,15(4):395-406
We have carried out a systematic study of buckling-like mechanical instabilities in simple two- (2D) and three-dimensional (3D) symmetric foam clusters sandwiched between parallel planar walls. These instabilities occur when the wall separation w is reduced below a critical value, w*, for which the foam surface energy E reaches its minimum, E*. The clusters under investigation consist of either a single bubble, or of twin bubbles of fixed equal sizes (areas A in 2D or volumes V in 3D), which are either free to slide or pinned at the confining walls. We have numerically obtained w* for both free and pinned 2D and 3D clusters. Furthermore, we have calculated the buckled configurations of 2D twin bubbles, either free or pinned, and of 3D free twin bubbles, whose energy is independent of w and equal to the minimum energy E* of the unbuckled state. Finally, we have also predicted the critical wt* at which the terminal configurations under extension of 2D and 3D single and twin bubbles are realised. Experimental illustrations of these transitions under compression and extension are presented. Our results, together with others from the literature, suggest that a bubble cluster bounded by two parallel walls is stable only if the normal force it exerts on the walls is attractive, i.e., if dE/dw > 0; clusters that cause repulsion between the walls are unstable. We correlate this with the distribution of film orientations: films in a stable cluster cannot be too parallel to the confining walls; rather, their average tilt must be larger than for a random distribution of film orientations. 相似文献
16.
A. Herlert L. Schweikhard M. Vogel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):65-68
Singly charged silver-cluster anions are produced in a laser vaporization source and transferred into a Penning trap. After
size selection the clusters are subjected to an electron bath in the trap, which results in the attachment of further electrons.
The relative abundance of dianions or trianions as a function of the clusters' size is analyzed by time-of-flight mass spectrometry.
Silver-cluster dianions are observed for sizes n≥ 24 and trianions for n > 100. In addition, a detailed study of the cluster sizes 24 ?n? 60 shows a pronounced resistance to electron attachment for singly charged anions Agn
- with a closed electronic shell, in particular Ag29
-, Ag33
-, and Ag39
-. Both the threshold size for the observation of dianionic silver clusters and the shell effects in the production yield correlate
favorably with previous theoretical investigations of the respective electron affinities.
Received 24 November 2000 相似文献
17.
V. Tevekeliyska Y. Dong M. Springborg V. G. Grigoryan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):19-22
In this work we present results from a theoretical study on the properties of sodium clusters. The structures of the global
total-energy minima have been
determined using two different methods. With the parameterized
density-functional tight-binding method (DFTB) combined with a genetic-algorithm we investigated the properties of NaN clusters with cluster size up to 20 atoms, and with our own Aufbau/Abbau algorithm together with the embedded-atom method (EAM) up to 60 atoms. The two sets of results from the
independent calculations are compared and a stability function is studied as function of the cluster size. Due to the electronic
effects included in the DFTB method and the packing effects included in the EAM we have obtained different global-minima structures
and different stability functions. 相似文献
18.
19.
C. Bobbert S. Schütte C. Steinbach U. Buck 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(2):183-192
The interaction of large ammonia and water clusters in the size range from <n> = 10 to 3 400 with electrons is investigated in a reflectron time-of-flight mass spectrometer. The clusters are generated
in adiabatic expansions through conical nozzles and are nearly fragmentation free detected by single photon ionization after
they have been doped by one sodium atom. For ammonia also the (1+1) resonance enhanced two photon ionization through the state with v = 6 operates similarly. In this way reliable size distributions of the neutral clusters are obtained which are analyzed in
terms of a modified scaling law of the Hagena type [Surf. Sci. 106, 101 (1981)]. In contrast, using electron impact ionization, the clusters are strongly fragmented when varying the electron
energy between 150 and 1 500 eV. The number of evaporated molecules depends on the cluster size and the energy dependence
follows that of the stopping power of the solid material. Therefore we attribute the operating mechanism to that which is
also responsible for the electronic sputtering of solid matter. The yields, however, are orders of magnitude larger for clusters
than for the solid. This result is a consequence of the finite dimensions of the clusters which cannot accommodate the released
energy.
Received 21 November 2001 相似文献
20.
R. Mitri C. Bürgel J. Burda V. Bonai-Koutecký P. Fantucci 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):41-44
Bimetallic silver-gold clusters are well suited to study
changes in metallic versus
ionic properties involving charge transfer as a function of
the size and the composition. We present structures, ionization
potentials (IP) and vertical detachment energies (VDE) for
neutral and charged bimetallic
AunAgm (
2(n +
m)5) clusters obtained from
density functional level of theory. In the stable structures of
these clusters Au atoms assume positions which favor charge
transfer from Ag atoms. In clusters with equal numbers of hetero
atoms (n =
m = 1- 4) heteronuclear
bonding is preferred to homonuclear bonding, giving rise to
large values of ionization potentials. For larger clusters
(n=m=5, 10) stable structures do not favor
neither hetero bonding nor segregation into the single
components, although they exhibit more metallic than ionic
features. This remains valid also for
Au8Ag12 cluster
characterized by strong charge transfer to gold subunit. The
influence of doping of pure gold clusters with silver atoms on
VDE and IP values is discussed in context of their reactivity
towards O2 and CO molecules. As a
starting point we consider reactivity towards CO and
O2 molecules on the example of
AgAu- dimer. The results show that
the catalytic cycle can be fullfilled. 相似文献