共查询到20条相似文献,搜索用时 62 毫秒
1.
V.Z. Cerovski S.D. Mahanti S.N. Khanna 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,10(1):119-122
Theoretical studies of the temperature (T) dependence of magnetization of Gd13 clusters have been carried out within a classical Heisenberg model using Monte-Carlo simulations. It is shown that for a
broad range of values of , defined as the ratio between competing ferro and anti-ferro magnetic couplings, the cluster magnetization increases with
T in the low T region, as seen in experiment. The clusters are also shown to exhibit a wide distribution of moments at a given T, which broadens significantly with increasing T. It is suggested that this may affect the observed magnetic behavior of magnetic clusters in Stern-Gerlach experiments.
Received 29 May 1999 and Received in final form 5 September 1999 相似文献
2.
E. Muñoz-Sandoval J. Dorantes-Dávila G.M. Pastor 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(1):89-96
The electronic and magnetic properties of clusters are investigated in the framework of the Hubbard model by treating electron
correlations effects in a saddle-point slave-boson approximation. The size dependent single-particle spectrum is calculated
using a third moment real-space expansion of the local density of states. Results for the magnetic moments, magnetic order,
average number of double occupations and hopping renormalizations are given as a function of the local coordination number
z, for different representative values of the Coulomb interaction strength U/t and band filling n. Several transitions between paramagnetic, ferromagnetic and antiferromagnetic behaviors are obtained as a function of z. The environment dependence of the magnetic behavior and of the degree of electron delocalization is analyzed. Advantages
and limitations of the present approach are discussed.
Received: 8 January 1998 / Revised: 22 June 1998 / Accepted: 6 August 1998 相似文献
3.
Magnetism in Rh clusters under hydrostatic deformations 总被引:1,自引:0,他引:1
E.O. Berlanga-Ramırez F. Aguilera-Granja A. Dıaz-Ortiz A. Vega 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):343-349
The magnetic behavior of rhodium clusters RhN (N = 4-38) under hydrostatic deformations was investigated. The starting cluster structures were obtained from an evolutionary
search algorithm applied to a Gupta potential. The spin-polarized electronic structure and related magnetic properties were
calculated using a self-consistent spd tight-binding Hamiltonian within the unrestricted Hartree-Fock approximation. The magnetic behavior was analyzed in terms
of the interdependence between the geometrical parameters and the electronic structure. Anomalous magnetic effects were found
in some cases.
Received 5 August 2002 / Received in final form 10 January 2003 Published online 4 March 2003
RID="a"
ID="a"e-mail: berlanga@dec1.ifisica.uaslp.mx 相似文献
4.
V. Boutou A.R. Allouche F. Spiegelmann J. Chevaleyre M. Aubert Frécon 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(1):63-73
The geometrical structure of ground state Ban clusters (n
=2-14) has been predicted from various types of calculations including two ab initio approaches used for the smaller sizes namely HF+MP2(
n
=2-6), DFT (LSDA)(
n
=2-6, 9) and one model approach HF+pairwise dispersion used for all sizes investigated here. The lowest energy configurations
as well as some isomers have been investigated. The sizes n
=4, 7 and 13 are predicted to be the relatively more stable ones and they correspond to the three compact structures: the tetrahedron,
the pentagonal bipyramid and the icosahedron. The growth behavior from Ba7 to Ba13 appears to be characterized by the addition of atoms around a pentagonal bipyramid leading to the icosahedral structure of
Ba13 which is consistent with the observed size-distribution of barium clusters. Values for vertical ionization potentials calculated
for n
=2-5 at the CI level are seen to be in quite good agreement with recent measures.
Received: 14 May 1997 / Received in final form: 2 February 1998 / Accepted: 27 February 1998 相似文献
5.
M. Acharyya D. Stauffer 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):571-575
We have studied the nucleation in the nearest neighbour ferromagnetic Ising model, in different (d) dimensions, by extensive Monte-Carlo simulation using the heat-bath dynamics. The nucleation time () has been studied as a function of the magnetic field (h) for various system sizes in different dimensions (d=2,3,4). The logarithm of the nucleation time is found to be proportional to the power (-(d-1)) of the magnetic field (h) in d dimensions. The size dependent crossover from coalescence to nucleation regime is observed in all dimensions. The distribution
of metastable lifetimes are studied in both regions. The numerical results are compared and found to be consistent with the
classical theoretical predictions. In two dimensions, we have also studied the dynamical response to a sinusoidally oscillating
magnetic field. The reversal time is studied as a function of the inverse of the coercive field. The applicability of the
classical nucleation theory to study the hysteresis and coercivity has been discussed.
Received: 21 January 1998 / Accepted: 17 March 1998 相似文献
6.
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
7.
Structure and magnetism on iron oxide clusters Fe nO m ( n = 1-5): Calculation from first principles
H. Shiroishi T. Oda I. Hamada N. Fujima 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):85-88
We have studied structural and magnetic properties in
small iron oxide clusters,
FenOm (n = 1-5), by means of the
first-principles calculation based on the density functional
theory. We have used not only the usual spin polarized scheme,
but also the scheme for noncollinear magnetism to carry out
efficient optimization in magnetic structure. The result of
FeOm (m
= 1-4) is in good agreement
with the previous work. We found the stable adduct clusters in
FeO5 and FeO6. The
bridge site of oxygen atom is more favorable in energy than any
other site for the clusters of FenO
(n
=
2-5). As increasing the number of oxygen atoms, the
alignment of Fe magnetic moments changes from ferromagnetic
configuration to antiferromagnetic one at
FenOn (n
=
2-4). Received 10 September 2002 Published online 3 July
2003 相似文献
8.
K. Hashimoto M. Okamoto K. Takayanagi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(1):75-78
The stability of neutral, singly and multiply ionized silicon clusters, (N
= 2-7, M
= 0, , , ), has been investigated using an ab initio density functional method. We show that the fragmentation effect significantly affects the structure of mass-spectra of multiply
ionized silicon clusters. For clusters, the clusters with a large fragmentation energy are found to correspond to the high peaks at N = 4 and 6 in mass-spectra. For clusters, a peak at N = 5 in mass-spectra has been predicted to be especially high.
Received: 9 June 1997 / Revised: 8 January 1998 / Accepted: 25 February 1998 相似文献
9.
A. Kanaev L. Museur F. Edery T. Laarmann T. Möller 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):261-268
We have studied the fluorescence of electronically excited OH*, H* and H2O+* dissociation fragments after VUV excitation ( h
ν≥11.6
eV) of rare-gas clusters (Rg = Ne, Ar) doped with H2O molecules. In contrast to a free molecule, where Balmer H-series dominate the UV-visible spectra, only the OH
*
(
A
2
Σ
+
↦
X
2
Π) emission band is observed in neon clusters. No emission of excited water ions has been observed. We find that while higher
excitation energies (Ne vs. Ar) induce higher vibrational excitation of the OH*
(
A
) fragment, the rotational temperature is lower. This effect is attributed to the difference in the geometric position of the
H2O molecule on the surface or inside the Rg-cluster. The rotational relaxation in neon clusters is rapid while the vibrational
relaxation is slow because of the coupling with the low energy matrix phonons.
Received 7 March 2002 / Received in final form 27 May 2002 Published online 19 July 2002 相似文献
10.
G.M. Koretsky M.B. Knickelbein 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(3):273-278
The photoionization spectra of Pr2-Pr21 and Ce2-Ce17 have been measured near threshold. The ionization potentials (IPs) of and vary discontinuously with size, but trend downward toward the work function of the bulk metals. In general, the IPs of cerium
clusters display more variation than those of praseodymium clusters. The sudden discontinuities observed in the IPs of both
and is akin to that displayed by clusters of transition metal atoms, suggesting that as in transition metal clusters, the rapid
evolution in geometric structure with size is the source of these discontinuities.
Received: 2 January 1998 / Accepted: 10 March 1998 相似文献
11.
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
12.
C.J. Calzado J.-P. Malrieu 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):375-381
Accurate ab initio calculations on embedded Cu4O12 square clusters, fragments of the La2CuO4 lattice, confirm a value of the nearest neighbor antiferromagnetic coupling (J
= 124 meV) previously obtained from ab initio calculations on bicentric clusters and in good agreement with experiment. These calculations predict non negligible antiferromagnetic
second-neighbor interaction (J'
= 6.5 meV) and four-spin cyclic exchange (K
= 14 meV), which may affect the thermodynamic and spectroscopic properties of these materials. The dependence of the magnetic
coupling on local lattice distortions has also been investigated. Among them the best candidate to induce a spin-phonon effect
seems to be the movement of the Cu atoms, changing the Cu-Cu distance, for which the variation of the nearest neighbor magnetic
coupling with the Cu-O distance is Δ
J
/Δ
d
Cu - O
∼ 1700 cm-1?-1.
Received 20 November 2000 相似文献
13.
M.P. Delamare G. Poullain C. Simon S. Sanfilippo X. Chaud A. Brûlet 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(1):33-38
An extensive study of small angle neutron scattering was performed in twinned YBa2Cu3O7 crystals in its superconducting state as a function of the angle between the c-axis of the crystal and the magnetic field. The half of the twin boundaries are oriented in the horizontal plane, which also
contains the neutron beam and the magnetic field. Two different diffraction patterns are studied as a function of at 5 K and B
= 0.5 T, one along the c-axis of the crystal, the other one along the applied field. These variations are interpreted in the model of accommodation
of the vortices on the twin planes by zigzagging from these planes to the ab-planes of the crystal, in order to minimize their energy.
Received: 9 March 1998 / Revised and Accepted: 12 June 1998 相似文献
14.
X.S. Chen V. Dohm 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):529-542
We derive exact results for several thermodynamic quantities of the O
(
n
) symmetric field theory in the limit in a finite d-dimensional hypercubic geometry with periodic boundary conditions. Corresponding results are derived for an O
(
n
) symmetric model on a finite d-dimensional lattice with a finite-range interaction. The leading finite-size effects near Tc of the field-theoretic model are compared with those of the lattice model. For 2 <
d
< 4, the finite-size scaling functions are verified to be universal. For d
> 4, significant lattice effects are found. Finite-size scaling in its usual simple form does not hold for d
> 4 but remains valid in a generalized form with two reference lengths. The finite-size scaling functions of the field theory turn out to be nonuniversal whereas those of the lattice model are independent of the nonuniversal model parameters. In particular, the field-theoretic model exhibits finite-size
effects whose leading exponents differ from those of the lattice model. The widely accepted lowest-mode approach is shown
to fail for both the field-theoretic and the lattice model above four dimensions.
Received: 20 October 1997 / Accepted: 5 March 1998 相似文献
15.
R. Guirado-López D. Spanjaard M.-C. Desjonquères 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(4):459-466
The magnetic properties of small YN clusters are studied by using a tight-binding Hubbard Hamiltonian in the unrestricted Hartree-Fock approximation. Several
types of cluster geometries are considered in order to see the effects of the size and symmetry of the structures on the magnetic
properties. The average magnetic moments are found to be constant over large domains of variations in the interatomic distance, a fact that can be explained by the
existing closed shell electronic configurations at least for one spin direction in all our magnetic solutions. Small energy
gains upon the onset of magnetization are obtained, which reveals the low stability of the magnetic solutions. Our results
contradict the prediction of a magnetic-nonmagnetic transition at a large cluster size (about 90 atoms) for these kinds of
systems.
Received: 27 April 1998 / Received in final form: 23 June 1998 / Accepted: 17 July 1998 相似文献
16.
E. M. Fernández G. Borstel J. M. Soler L. C. Balbás 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):245-248
The ionic and electronic structure of
(Al2O3)n(Ox)
clusters with n
16 and x
= 0,
1, 2 is studied by means of first principles density functional
calculations, norm-conserving pseudopotentials and a numerical
atomic basis set. The equilibrium geometries have been
determined by total energy minimization, starting with several
initial geometries for each cluster size. The trends obtained
for the atomic arrangements (structural isomers, coordination
numbers, disordered versus
ordered structures, etc.) and the electronic properties
(binding energies, Homo-Lumo gap and dipole moments) are
discussed. For most of the oxidized clusters studied here we
find that the Homo-Lumo gap and the magnitude of dipole moment
of isomeric species can vary drastically. 相似文献
17.
P. Mierzyński K. Pomorski 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(3):311-314
Strutinsky shell corrections for the cesium-coated fullerenes were investigated. The single particle levels of electrons are
obtained using the spherical mean-field potential of a shifted Wood-Saxon type. The parameters of the potential are adjusted
to reproduce the experimental ionization energies of the Cs(N) clusters and the magic numbers observed in their photo-ionization spectra of the C60Cs(N) aggregates.
Received 24 May 2002 / Received in final form 9 July 2002 Published online 15 October 2002
RID="*"
ID="*"This work has been partly supported by the Polish Committee for Scientific Research under Contract No. 2P03B 115 19
and by the Program of Scientific Exchange between the IN2P3-France and the Polish Research Institution No. 99-95.
RID="b"
ID="b"e-mail: Krzysztof.Pomorski@umcs.lublin.pl 相似文献
18.
P. Parneix 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):375-383
The isomerization and evaporation processes in the neutral homogeneous (CH3CN)n molecular clusters (n
= 2-7) have been investigated using classical molecular dynamics simulations. The evaporation rate constants and the kinetic energy
release in the dissociation have been analysed as a function of the cluster size and as a function of the internal energy
in the parent cluster. The competition between monomer and dimer ejections has been also carefully studied. All the dynamical
properties in these dissociative processes have been discussed in relation to the static properties of the clusters involved
in the dissociation and also in relation to the solid-liquid like transition which appears in these homogeneous molecular
clusters.
Received 19 November 2002 / Received in final form 5 February 2003 Published online 29 April 2003
RID="a"
ID="a"e-mail: pascal.parneix@ppm.u-psud.fr
RID="b"
ID="b"Laboratoire associé à l'université Paris-Sud. 相似文献
19.
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
20.
E. Rastelli A. Tassi 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):285-289
Dipolar spin-spin interactions play a crucial role as for the magnetic order in the compounds of the RBa2Cu3O6+x family, (R = Dy, Er, Nd). However, inelastic neutron scattering data observed in ErBa2Cu3O7 can be explained only if exchange interactions in addition to dipolar ones are taken into account.
Received: 12 January 1998 / Received in final form: 26 March 1998 / Accepted: 10 April 1998 相似文献