共查询到20条相似文献,搜索用时 15 毫秒
1.
F. Aguilera-Granja A. Vega J. Rogan W. Orellana G. García 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(1):125-131
We report a comparative study of the magnetic properties of
free-standing PdN clusters (2 ≤N ≤21) obtained
through two different theoretical approaches that are extensively
employed in electronic structure calculations: a semi-empirical
Tight-Binding (TB) model and an ab-initio DFT pseudopotential
model. Conclusions are drawn about the reliability of the TB model for
the investigation of the electronic structure and magnetic properties
of such complex 4d Transition Metals (TM) systems and we compare the
results with previous systematic DFT calculations and comment on some
available experiments in the literature. 相似文献
2.
J. Zhang D. Repetto V. Sessi J. Honolka A. Enders K. Kern 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):515-520
The growth and magnetism of nanometer size Fe clusters on stepped Pt surfaces is investigated by scanning tunneling microscopy
(STM) and magneto-optical Kerr effect measurements (MOKE). The clusters are formed on xenon buffer layers of varying thickness
and then brought into contact with the substrate by thermal desorption of the Xe. The cluster size is controlled by the thickness
of the Xe layer. It is found that clusters of diameter smaller than the Pt terrace width of 2 nm are aligned along the step
edges of the Pt(997), thus forming linear cluster chains. In this arrangement, the clusters are ferromagnetic with an easy
axis in the direction along the surface normal. If the cluster diameter is larger than the terrace width then the alignment
along the step edges is not observed and rather large agglomerates are found which are randomly distributed over the surface.
Despite their increased volume, such agglomerates are superparamagnetic with in-plane easy magnetization axis. The enhanced
magnetic anisotropy energy in the smallest clusters is originating from hybridization effects at the Fe-Pt interface. 相似文献
3.
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
4.
A. Rytkönen M. Manninen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):351-357
The effect of melting transition on the ionization potential has been studied for sodium clusters with 40, 55, 142, and 147
atoms, using ab initio and classical molecular dynamics. Classical and ab initio simulations were performed to determine the ionization potential of Na142 and Na147 for solid, partly melted, and liquid structures. The results reveal no correlation between the vertical ionization potential
and the degree of surface disorder, melting, or the total energy of the cluster obtained with the ab initio method. However, in the case of 40 and 55 atom clusters, the ionization potential seems to decrease when the cluster melts.
Received 1st November 2002 Published online 24 April 2003
RID="a"
ID="a"e-mail: ar@phys.jyu.fi 相似文献
5.
C. Bréchignac Ph. Cahuzac B. Concina J. Leygnier 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):91-94
We have studied experimentally the collisional charge transfer between a neutral atom and a multicharged metal-atom cluster.
The charge transfer cross section measured for Na 31
+ + + Cs is in the range of 400 ?2. The time-of-flight mass analysis of the singly charged collision products demonstrates that an energy of about 0.5 eV is
deposited in the cluster fragment during the charge transfer collision. This effect can be interpreted as a charge transfer
to an excited state of the metal cluster. The measured cross section for Na 31
+ + + Cs is larger than the one for Na 31
+ + Cs collisions. This difference between these two systems is due to the existence, for the first one, of a Coulombic repulsion
term in the collision output channel.
Received 24 October 2000 相似文献
6.
Metallic evolution of small magnesium clusters 总被引:1,自引:0,他引:1
J. Akola K. Rytkönen M. Manninen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):21-24
Structural and electronic properties of small magnesium clusters (N≤13) are studied using a first-principles simulation method in conjunction with the density functional theory and generalized
gradient correction approximation for the exchange-correlation energy functional. It is observed that the onset of metallization
of magnesium clusters is hard to assign since both the s-p hybridization and the energy gap between the valence and conduction bands do not evolve rapidly towards the known bulk properties.
Instead these quantities show a slow and nonmonotonic evolution.
Received 15 November 2000 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.
T. Döppner Th. Diederich J. Tiggesbäumker K.-H. Meiwes-Broer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):13-16
Magnesium clusters grown in helium droplets and ionized with femtosecond laser pulses have been studied by high resolution
mass spectrometry. For moderate laser intensities the abundance spectra show characteristic features indicating electronic
shell effects. Compared to clusters of s1-electron metals additional shell closures appear resulting from an electron rearrangement. Irradiation with higher laser
intensities leads to a decomposition of the magnesium clusters into atomic ions. Due to charge exchange with the surrounding
helium matrix mainly singly and doubly charged magnesium ions remain. In addition, the occurrence of MgHeN
+-complexes is observed. Their abundance depends on the shape of the laser field, i.e. the laser width and the optical delay when applying the pump-probe technique.
Received 2 January 2001 相似文献
9.
S. Dennler J. L. Ricardo-Chavez J. Morillo G. M. Pastor 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):237-240
Structural and magnetic properties of small bimetallic
clusters like
CoMRhN,
NiNaN, and NiCuN
are determined in the framework of a generalized
gradient-corrected approximation to density functional theory.
The role of magnetism on the most stable structure and on the
energy differences among the low-lying isomers is quantified by
comparing magnetic and non-magnetic solutions of the Kohn-Sham
equations. The correlation between structure, chemical order,
and environment-dependent magnetic properties is discussed. 相似文献
10.
R. Guirado-López D. Spanjaard M.-C. Desjonquères A.M. Oleś 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(4):437-446
We analyze the stability of magnetic states obtained within the tight-binding model for cubooctahedral (Oh) and icosahedral (Ih) clusters of early 4d (Y, Zr, Nb, Mo, and Tc) transition metals. Several metastable magnetic clusters are identified which suggests the existence
of multiple magnetic solutions in realistic systems. A bulk-like parabolic behavior is observed for the binding energy of
Oh and Ih clusters as a function of the atomic number along the 4
d-series. The charge transfer on the central atom changes sign, while the average magnetic moments present an oscillatory behavior
as a function of the number of d electrons in the cluster. Our results are in agreement with other theoretical calculations.
Received: 20 November 1997 / Received in final form: 9 March 1998 / Accepted: 30 March 1998 相似文献
11.
G. Ballentine M. Heßler M. Kinza K. Fauth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):535-537
Fe clusters of 105±2 atoms/cluster were mass selectively deposited onto Cu(111) at cryogenic temperatures.
XMCD was used to measure temperature and direction dependent magnetization curves.
The clusters are superparamagnetic at the lowest temperature measured (10 K). Their magnetization curves are consistent with
magnetic moments of ≈2.5μB per atom which are thus enhanced over the bulk values.
Within experimental accuracy, the clusters do not present magnetocrystalline anisotropy in the temperature range
of 10 K to 60 K. 相似文献
12.
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
13.
R.J. Tarento P. Joyes J. van de Walle 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(3):355-360
The present study focuses on electronic correlation effects on magnetic energy, the spin-spin correlation function of an octahedron
cluster in the (3↑, 3 ↓) electronic configuration threaded by a magnetic field. Some other spin configurations are also discussed
and various field directions are considered. An accurate diagonalisation technique has been used to solve the Hubbard Hamiltonian.
A result is analysed on a linear energy stabilisation at low magnetic flux. Moreover, two types of antiferromagnetic transition
versus the flux occurring for a correlation term larger than a critical one have been observed, i.e. the likelihood of a charge excitation before the antiferromagnetic transition. Finally, a comparison between the results
obtained from the exact diagonalisation and the Gutzwiller method has been carried out, leading to a suggested modification
of the Gutzwiller approach in order to improve it.
Received 23 June 1999 and Received in final form 28 July 2000 相似文献
14.
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
15.
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
16.
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
17.
F. Hagelberg C. Xiao B. Marsen M. Lonfat P. Scheier K. Sattler 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(1):37-41
In a series of recent experiments, the HOMO-LUMO energy gaps of small Si clusters deposited on a graphite substrate have been
determined by Scanning Tunneling Microscopy (STM). The values obtained were found to be substantially smaller than the energy
gaps of corresponding passivated clusters. This work considers dimensional reduction as a possible mechanism for a sizeable
energy gap narrowing by the example of the system Si5. The impact of the graphite substrate on the deposited species is investigated in the framework of a pseudocluster model.
Received 30 November 2000 相似文献
18.
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
19.
B. Pilawa I. Keilhauer G. Fischer S. Knorr J. Rahmer A. Grupp 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(3):321-330
The magnetic properties of the cyclic compound [Fe6(bicine)6] LiClO4
. 2MeOH are reported. The cluster Fe6(bicine)6 forms an antiferromagnetically coupled ring structure of Fe III ions. The magnetic susceptibility is measured between 2 and 300 K and yields the exchange coupling of J/k
B = - 27.5±0.5 K. The field dependence of the magnetic moment is studied at 3 and 6 K in magnetic fields up to 5 T. The zero-field
splitting of the first excited spin states with S = 2 and 3 are determined by ESR at 94 GHz. The intra-molecular interactions of the Fe III ions are analyzed and the on-site anisotropy of the Fe III due to the ligand-configuration is determined to d /k
B = - 0.633±0.008K.
Received 28 October 2002 / Received in final form 22 February 2003 Published online 20 June 2003
RID="a"
ID="a"e-mail: bernd@piobelix.physik.uni-karlsruhe.de 相似文献
20.
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