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1.
Energetic and entropic influences on the melting temperatures of size selected sodium clusters are experimentally separated. It is shown that the energetic difference between solid and liquid is the leading influence for the still puzzling features in the size dependence of sodium melting points. Additionally, this energy difference decreases towards smaller cluster sizes and causes steplike melting phase transitions to vanish. The entropy difference between solid and liquid has been found to be strongly correlated with the energy and causes a pronounced damping of the energetic influences. 相似文献
2.
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
3.
采用密度泛函理论(DFT)B3LYP方法在6-311+G(d,p)基组水平,对CaSi_n(n=1~10)的结构进行优化,得出各个尺寸下团簇处于最低能量的结构模型,并对其稳定性等物理化学性质进行理论研究,表明CaSi_2、CaSi_5和CaSi_9为幻数团簇. 相似文献
4.
运用距离相关紧密结合的分子动力学模型,通过无量纲的形变参数S1对简单金属原子团簇Na4、Na8、Na14和Na20相变时的多极形变特征进行了分析,发现S1可以用作表征团簇形变的灵敏探针. 相似文献
5.
A minimal parameter tight binding molecular dynamics scheme is used to study Cu
n
clusters with
. We present results for relaxed configurations of different symmetries, binding energies, relative stabilities and HOMO-LUMO gap energies for these clusters. Detailed comparison for small clusters n = 3-9 with ab initio and available experimental results shows very good agreement. Even-odd alternation due to electron pairing and magic behaviour for Cu2, Cu8, Cu18 and Cu20 due to electronic shell closing are found. We found electronic effects, electronic shell closing and electron pairing in the HOMO dominates over the geometrical effect to determine the relative stability of copper clusters. The present results indicate that tight-binding molecular dynamics scheme can be relied on to provide a useful semiempirical scheme in modeling interactions in metallic systems.Received: 3 May 2004, Published online: 26 October 2004PACS:
36.40.Cg Electronic and magnetic properties of clusters - 36.40.Mr Spectroscopy and geometrical structure of clusters - 36.40.Qv Stability and fragmentation of clusters 相似文献
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On the basis of density-functional theory (PW91) and an all-electron numerical basis set, 60 optimized structures of Fe3O3+ clusters were obtained through optimization calculation and frequency analysis of 216 initial structures. 28 different isomers were ultimately confirmed after analyzing and re-calculating. The binding energies, the energy gaps between the highest occupied molecular orbital and lowest unoccupied molecular orbital, and the total magnetic moments of all stable isomers are reported. Some discussion of the relationship between electronic properties and structures is also presented. 相似文献
10.
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
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C. H. Yao S. F. Zhao J. R. Li Y. W. Mu J. G. Wan M. Han G. H. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,57(2):197-205
The lowest-energy geometries and electronic-structure properties have been
obtained for AlnHn (n=1-10) clusters within the
density-functional theory using the generalized gradient approximation for
the exchange correlation potential. The resulting geometries show that the
hydrogen atoms tend to occupy outside positions and no hollow positions are
found. The subunit Aln of AlnHn (n=1-5) have little
distortion, in comparison with corresponding pure Aln cluster, whereas
the subunit Aln have large distortion from n=6. The stability has been
investigated by analyzing the binding energy per atom and the second
difference in energy, indicating that Al8H8 exhibit higher
stability than others. The bonding property has been analyzed by calculating
the Mulliken charges and Al–H distances. The calculated energy gap between
the highest occupied molecular orbital and the lowest unoccupied molecular
orbital (HOMO-LUMO), the vertical ionization potential, and the vertical
electron affinity also confirm that Al8H8 is a stable cluster. The
density of states (DOS) shows that AlnHn exhibit changes from
molecular-like (Al1H1) to band-like structure (Al10H10)
as n increases. 相似文献
16.
E. G. Noya J. P.K. Doye D. J. Wales A. Aguado 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):57-60
Putative global minima
of sodium clusters with up to 380 atoms
have been located for two model interatomic potentials in
order to identify the structures responsible for the size-dependence
of the thermodynamic properties in experiments.
Structures based upon the Mackay icosahedra predominate for both potentials,
and the magic numbers for the Murrell-Mottram model show excellent
agreement with the sizes at which maxima in the latent heat and entropy
change at melting have been found in experiment. In particular,
the magic numbers at sizes intermediate between the complete Mackay icosahedra
are due to unusual twisted icosahedral structures. 相似文献
17.
Dafang Li Baotian Wang Hongliang Shi Shaoping Zhu Ping Zhang 《Physics letters. A》2010,374(43):4458-4464
Based on the density functional theory, we systematically study the optical and electronic properties of the insulating dense sodium phase (Na-hp4) reported recently (Ma et al., 2009). The structure is found optically anisotropic. Through Bader analysis, we conclude that ionicity exists in the structure and becomes stronger with increasing pressure. 相似文献
18.
Armen Melikyan Hayk Minassian Valeri G. Grigoryan Michael Springborg 《Applied physics. B, Lasers and optics》2013,112(2):177-184
We develop an analytical approach to calculate the aspect ratios of free alkali metal clusters using measured surface plasmon frequencies. The method is based on the concept of small deviations from a spherical shape and can be applied to clusters with spheroidal, icosahedral and other shapes. Results of experimental data as well as of numerical calculations for the surface plasmon resonance frequencies in small spheroidal sodium clusters containing less than 50 atoms are reproduced accurately through a quite simple formula which links the aspect ratio of the cluster to the observable surface plasmon frequencies. The developed approach allows also to reveal the dependence of the dielectric function of alkali metal on the number of atoms in the cluster. 相似文献
19.
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
20.
Geometric, electronic and vibrational properties of the most stable and energetically favourable configurations of indium oxide clusters InmOn (1≤m, n≤4) are investigated using density functional theory. The lowest energy geometries prefer the planar arrangement of the constituent atoms with a trend to maximize the number of ionic In-O bonds. Due to the charge transfer from In to O atoms, the electrostatic repulsion occurs between the atoms with the same kind of charge. The minimization of electrostatic repulsion and the maximization of In-O bond number compete between each other and determine the location of the isometric total energy. The most stable linear In-O-In-O structure of In2O2 cluster is attributed to the reduced electrostatic repulsive energy at the expense of In-O bond number, while the lowest energy rhombus-like structure of In2O3 cluster reflects the maximized number of In-O bonds. Furthermore, the vibrational frequencies of the lowest energy clusters are calculated and compared with the available experimental results. The energy gap and the charge density distribution for clusters with varying oxygen/indium ratio are also discussed. 相似文献