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Showing papers on "Cluster (physics) published in 1975"


Journal ArticleDOI
TL;DR: In this paper, the surface energies of the microclusters were expressed as a function of the form Ai2/3+Bi1/3 where i is the number of atoms in the cluster.
Abstract: Microclusters of 2–100 argon atoms were studied using molecular dynamics. The microclusters were ordered solids at low temperatures and energies and disordered liquids at high temperatures and energies. The melting transition occurred considerably below the bulk melting temperature. Radial density functions, interference functions, diffusion coefficients, and surface energies were calculated for both the solid and liquid phases. The surface energies of the microclusters could be expressed as a function of the form Ai2/3+Bi1/3 where i is the number of atoms in the cluster. For 0 °K solid clusters A and B have the values 0.26×10−12 and −0.12×10−12 erg, respectively; for liquid clusters at 40 °K, A and B have the values 0.17×10−12 and −0.045×10−12 erg, respectively. Clusters containing 7 or more atoms melted with the occurence of a first‐order‐like transition. This transition was studied further through Monte Carlo calculations. A possible model for the first‐order‐like transition is proposed.

313 citations


Journal ArticleDOI
TL;DR: The interaction site cluster expansion (ISCE) series as mentioned in this paper provides an exact formula for the equilibrium pair correlations between interaction sites on different molecules for a general class of molecular models, where each molecule contains m of these interaction sites and the total intermolecular potential between two molecules is the sum of m 2 site-site potentials.
Abstract: A new cluster series, called the interaction site cluster expansion, is derived for classical molecular fluids. For a general class of molecular models, the series provides an exact formula for the equilibrium pair correlations between interaction sites on different molecules. In the models considered, each molecule contains m of these interaction sites. The total intermolecular potential between two molecules is the sum of m2 site–site potentials. A site–site potential depends on the separation between the sites only. However, because the sites are not necessarily located at the centers of molecules, the total molecular pair interaction can depend strongly on molecular orientations. Even though the interaction site cluster expansion is exact, the cluster integrals in the series involve the translational coordinates of the interaction sites only. The molecular orientational coordinates are removed by a transformation which introduces intramolecular correlation functions into the series. Thus, the new clus...

200 citations


Journal ArticleDOI
TL;DR: In this paper, the Born model is used to examine the possible structures of defect clusters in non-stoichiometric FeO. The basic defect cluster is identified as a complex of four cation vacancies and one tetrahedral Fe3+ ion.
Abstract: Lattice energy calculations based on the Born model are used to examine the possible structures of defect clusters in non-stoichiometric FeO. The basic cluster is identified as a complex of four cation vacancies and one tetrahedral Fe3+ ion (or 4:1 cluster) which is formed as a result of a large Coulomb term favouring the occupation of the tetrahedral site when all nearest-neighbour cations are vacant. The aggregation of these 4:1 clusters occurs by vacancy-sharing, and the calculations suggest that the most stable small aggregates are formed by edge- rather than corner-sharing (6:2 or 8:3 clusters). If more extended clusters are formed they are likely to involve corner-sharing, but the binding energy for a cluster closely related to the Fe3O4 structure is larger than that calculated for the Koch-Cohen cluster.

158 citations


Journal ArticleDOI
M.R. Hoare1, P. Pal1
TL;DR: In this article, the authors extended previous computations of atomic microclusters to the realm of statistical thermodynamics, obtaining thermodynamic functions for small, solid-like Van der Waals clusters of less than some 100 atoms possessing non-crystalline structures of "polytetrahedral" type.
Abstract: We extend previous computations of mechanical stability of atomic microclusters to the realm of statistical thermodynamics, obtaining thermodynamic functions for small, solid-like Van der Waals clusters of less than some 100 atoms possessing non-crystalline structures of ‘polytetrahedral’ type. These are shown to be almost invariably at a thermodynamic advantage over alternative lattice structures of the same number of atoms, at least for the Lennard-Jones potential in the harmonic-oscillator/rigid-rotor approximation. The dependence of thermodynamic functions upon cluster size appears to be essentially monotonic in the number of internal degrees of freedom; although there are certain exceptional structures, particularly with icosahedral symmetry, there proves to be little evidence for the occurrence of ‘magic numbers’ for stability at any temperature and within the size-range considered. Particular attention is given to the heat capacity of model systems in relation to their vibrational spectra....

150 citations


Journal ArticleDOI
TL;DR: The Mössbauer investigation reveals three other spectral components characteristic of iron nuclei in an environment of integer or zero electronic spin, i.e. they reside in complexes which are "EPR-silent".

147 citations


Journal ArticleDOI
TL;DR: In this article, a simple analytical expression is obtained for the distribution function of any cluster in the high energy limit, and a comparison of this expression with experimental data on the energy and angle distribution of Wk + clusters at high energies shows good agreement.
Abstract: Our previous model on dimer sputtering is extended to the formation of larger clusters. The general formalism for the calculation of the momentum distribution function of these clusters is given. A simple analytical expression is obtained for the distribution function of any cluster in the high energy limit. Comparison of this expression with experimental data on the energy and angle distribution of Wk + clusters at high energies shows good agreement. The experimental results on K2 and KI sputtering with low energies are recompared with the theory. For the ionic crystal KI, evidence is obtained that sputtering of non adjacent K and I atoms from the lattice gives an important contribution to dimer formation. The role of the binding energy Eb , of the particles with respect to the surface is discussed.

136 citations


Journal ArticleDOI
TL;DR: In this article, the equilibrium thermodynamic properties of small clusters of xenon, krypton, and argon atoms, determined from a biased random-walk Monte Carlo procedure, were reported.
Abstract: The present work reports on the equilibrium thermodynamic properties of small clusters of xenon, krypton, and argon atoms, determined from a biased random-walk Monte Carlo procedure. Cluster sizes ranged from 3 to 13 atoms. Each cluster was found to have an abrupt liquid-gas phase transition at a temperature much less than for the bulk material. An abrupt solid-liquid transition is observed for thirteen- and eleven-particle clusters. For cluster sizes smaller than 11, a gradual transition from solid to liquid occurred over a fairly broad range of temperatures. Distribution of number of bond lengths as a function of bond length was calculated for several systems at various temperatures. The effects of box boundary conditions are discussed. Results show the importance of a correct description of boundary conditions. A surprising result is the slow rate at which system properties approach bulk behavior as cluster size is increased.

123 citations





Patent
23 Oct 1975
TL;DR: In this article, an ion source called "Vaporized-metal cluster ion source" is adapted to produce ionized vapor aggregate (ionized cluster) instead of atomic or molecular ions in conventional ion sources.
Abstract: The present ion source called "Vaporized-Metal Cluster Ion Source" is adapted to produce ionized vapor aggregate (ionized cluster) instead of atomic or molecular ions in conventional ion sources. Clusters consisting of 10 2 -10 3 atoms are formed by the adiabatic expansion due to the ejection into a high vacuum region through a nozzle of a heated crucible and ionized by electron bombardment. By "Ionized-Cluster Beam Deposition" using the ion source, fine-quality deposited films of many kinds of materials can be obtained on metal, semiconductor and insulator substrate with strong adhesion and with a fairly high deposition rate.

Journal ArticleDOI
TL;DR: In this paper, a method for studying the electronic structure of binary alloys within the tight-binding framework is presented and developed in detail, which involves treating part of the system exactly as a cluster of atoms and simulating the rest of the environment by connecting to each atom at the surface of the cluster a Bethe lattice of the same coordination number.
Abstract: A new method for studying the electronic structure of binary alloys within the tight-binding framework is presented and developed in detail. The method involves treating part of the system exactly as a cluster of atoms and simulating the rest of the environment by connecting to each atom at the surface of the cluster a Bethe lattice of the same coordination number. The method includes from its inception the idea of short-range correlation effects of a nearest-neighbor order parameter. Clusters of different size have been studied and analyzed in detail. An illustrative example is presented to show the striking differences which appear in various concentration sequences. These sequences are selected to be (i) random, (ii) with a tendency to segregation, and (iii) with a tendency to form binary compounds. The results emphasize the need to include short-range correlation effects when dealing with alloys. The method also provides a clear identification of localized states. In addition, it gives very naturally the position of band edges and energy gaps. The method, when averaged over all alloys with equal concentration and all short-range order parameters, reproduces in a satisfactory way the results of the single-site coherent-potential approximation.



Journal ArticleDOI
TL;DR: In this paper, the electronic structures and binding energies of eight clusters of lithium, namely Li2, Li3 (triangular), Li4 (square), Li 4 (tetrahedral), Li8 (simple cubic), Li9 (cubo-octahedral) and Li13 (icosahedral), have been calculated as a function of the LiLi bond distance by the recently developed SelfConsistent Field Xα Scattered-Wave Method.



Journal ArticleDOI
TL;DR: The electronic structure and charge distributions for 13-atom clusters of 3D transition metals (Fe, Ni, and Cu) have been calculated using a scattered wave technique as mentioned in this paper, and the cluster geometry is chosen to display features of stepped and flat surfaces.

Journal ArticleDOI
TL;DR: In this article, the preparation and properties of polynuclear carbonylhydrido complexes (NEt4)3[H4Re4(OCH3)(CO)16] (I) and NEt4(2]2 [H4 Re4(CO)15] (II) are reported.

Journal ArticleDOI
TL;DR: In this paper, a simple model with three variable parameters was developed for calculating observed clustering data from a free jet expansion, and the reactive cross sections that gave the best fit of experimental data were given by (π/4) σ2R1 = 9.90×10−16 cm2 and (π /4) ε2R3=5.22 ×10−17 cm2.
Abstract: A simple model with three variable parameters is developed for calculating observed clustering data from a free jet expansion. One parameter, σR1, can be associated with a reactive collision diameter for a monomer associating with a cluster to form a larger, excited cluster. A second parameter, σR3, can be associated with a reactive collision diameter for energy transfer from the excited cluster to the surrounding gas. The third parameter, K′, is a constant in a unimolecular decay rate expression for the excited cluster. The reactive cross sections that give the best fit of experimental data are given by (π/4) σ2R1 =9.90×10−16 cm2 and (π/4) σ2R3=5.22 ×10−17 cm2. No value could be assigned to K′. Apparently the excited clusters are stabilized by energy exchange collisions in this particular flow field before there is appreciable unimolecular decay. Good fits of clustering data are obtained even though these same values are used for clusters varying in size from 6 to 26 water molecules. Since the clustering...

Journal ArticleDOI
TL;DR: In this article, a model for discussing deep defect levels in covalent solids, based on the representation of the one−electron energies of the crystal by the eigenvalue spectrum of a small periodic cluster of atoms, was proposed.
Abstract: A model is proposed for discussing deep defect levels in covalent solids, based on the representation of the one−electron energies of the crystal by the eigenvalue spectrum of a small periodic cluster of atoms. Calculations of this model by semiempirical MO−LCAO methods for a vacancy problem in hexagonal boron nitride and graphite and substitutional boron impurity in graphite, yield satisfactory results when compared with experimental EPR, thermoluminescence, and thermally−stimulated−currents data.

Journal ArticleDOI
TL;DR: In this paper, the evolution of a cluster by a postulated stochastic master equation in which the transition probabilities are given by a formula proposed by Langer is described. And they derive from these assumptions, by a path integral method, an equation for the most probable evolution of the size of the cluster and show thereby that under these circumstances the two definitions are equivalent.
Abstract: A critical cluster in homogeneous nucleation can be defined in two ways. Thermodynamically, the size of the critical cluster corresponds to a maximum of the free energy of the system; kinetically the critical cluster is defined such that all supercritical clusters grow and all others decay. We describe the evolution of a cluster by a postulated stochastic master equation in which the transition probabilities are given by a formula proposed by Langer. We derive from these assumptions, by a path integral method, an equation for the most probable evolution of the size of the cluster and show thereby that under these circumstances the two definitions are equivalent.

Journal ArticleDOI
TL;DR: In this article, the electronic levels and the total energies for a series of chalcogen−nickel clusters were calculated by the self-consistent field Xα scattered−wave method.
Abstract: The electronic levels and the total energies for a series of chalcogen−nickel clusters are calculated by the self−consistent field Xα scattered−wave method. In accord with experimental results the chalcogen atoms are assumed to be located in a pyramidal position above a cluster of nickel atoms whose geometry simulates the (001) surface of nickel. Binding energy curves of the clusters are calculated for various positions of each of the chalcogens above the Ni ’’surface.’’ The resulting favored positions are compared with those obtained experimentally. The characteristics of the orbitals directly involved in the binding of the chalcogen to the nickel cluster are discussed.

Journal ArticleDOI
L. Malatesta1
TL;DR: In this article, the authors reviewed the work carried out under his direction in the laboratory of the Italian Research Council on the structure of an unusual class of compounds in which metal atoms in zero or low oxidation states are bonded to one another.
Abstract: In this paper the author reviews the work carried out under his direction in the laboratory of the Italian Research Council on the structure of an unusual class of compounds in which metal atoms in zero or low oxidation states are bonded to one another. The resolution of the configuration of the atoms in these interesting compounds may well improve our understanding of the electronic structure of metals and alloys.

Journal ArticleDOI
TL;DR: In this paper, an ab-initio cluster calculation of the electronic d-states in VO$sub 2$ has been made by using the selfconsistent statistical exchange multiple scattering method.
Abstract: An ab-initio cluster calculation of the electronic d-states in VO$sub 2$ has been made by using the self-consistent statistical exchange multiple scattering method. VO$sub 6$$sup 8-$ octaedron was used to represent the tetragonal phase, and a V$sub 2$O$sub 10$$sup 12-$ cluster with paired vanadium atoms was used for the monoclinic phase. Our results are in conflict with an explanation of the semiconducting gap in terms of simple distortion-induced band splitting. (FR)

Journal ArticleDOI
TL;DR: For example, the authors found that a majority of subjects were willing to administer what they believed to be painful and dangerous electric shocks, even when the victim was crying out in protest and agony.
Abstract: source of authority was an ordinary man without official position, if two sources of authority gave incompatible orders, and if there were other people around who protested at the idea of carrying on with the punishment. However, to the world at large and to Milgrani himself the most startling finding of the whole series of experiments was the willingness of a majority of subjects under standard conditions to administer what they believed to be painful and dangerous electric shocks, even when the victim was †̃¿ crying out in protest and agony'. Why this should so surprise us who have lived in a twentieth century of totalitarian states is itself something of a mystery. The experiments are well worth writing up in book form, in that they confront us with a dramatic presentation, within the laboratory, of a fundamental human situation. They have generated fierce argu ment—a proper purpose of psychological experi.. ments. The argument has included strong attacks on Milgram's own morality in deceiving (some say cruelly deceiving) his subjects. It may be that in so doing Milgram was, like his subjects, only manifesting obedience to the authority of †̃¿ Science'. The wealmess of the work lies in its lack of an elaborated theoretical base. †̃¿ Obedience' is a concept which obviously covers a multitude of psychological sins and is not to be explained by another equally global concept of †̃¿ authority'. Milgram's subjects were not simply obeying the authority of an experi menter in a white coat—they were obeying the authority of a whole culture which has given them

Journal ArticleDOI
TL;DR: In this paper, the reaction 6 Li(γ, t) 3 He has been studied from E γ = 18 to 70 MeV by electrodisintegration and various dipole sum rules obtained from the experimental results are consistent with the 3 H + 3 He cluster description of 6 Li.

Journal ArticleDOI
TL;DR: In this paper, the synthesis, spectroscopic features and crystal structure of a new heteronuclear cluster compound [P(C6H5)3]2Pt2C02(CO)8 of butterfly type are reported.

Journal ArticleDOI
TL;DR: In this article, a stable pair potential with finite range was considered for R d systems of particles in R d and they were investigated by subdividing every particle configuration into clusters of interacting particles and studying the cluster distributions corresponding to equilibrium particle distributions.
Abstract: We consider classical systems of particles in R d interacting by a stable pair potential with finite range. We are engaged in subdividing every particle configuration into clusters of interacting particles and studying the cluster distributions corresponding to equilibrium particle distributions.