Showing papers on "Cluster (physics) published in 1974"
TL;DR: In this paper, the size distribution and growth in the gas phase of ions in the series H+(H2O)n were investigated. But the results were limited to n = 28.
Abstract: This paper presents results concerning size distribution and growth in the gas phase of ions in the series H+(H2O)n. The measurements span a range of cluster sizes up to n =28, a domain not previously investigated quantitatively. The molecular beam sampling technique developed for this study promises to be a powerful tool in the study of ion nucleation phenomenon. Noteworthy observations include the unusual stability of the cluster with n =21 and the absence of trapped molecules of carrier gas within a cluster.
271 citations
01 Aug 1974
TL;DR: In this article, the size distribution and growth in the gas phase of ions in the series H+(H2O)n were investigated. But the results were limited to n = 28.
Abstract: This paper presents results concerning size distribution and growth in the gas phase of ions in the series H+(H2O)n. The measurements span a range of cluster sizes up to n =28, a domain not previously investigated quantitatively. The molecular beam sampling technique developed for this study promises to be a powerful tool in the study of ion nucleation phenomenon. Noteworthy observations include the unusual stability of the cluster with n =21 and the absence of trapped molecules of carrier gas within a cluster.
253 citations
233 citations
TL;DR: In this article, a renormalization-group technique is used to study the critical behavior of spin models in which each interaction has a small independent random width about its average value.
Abstract: A renormalization-group technique is used to study the critical behavior of spin models in which each interaction has a small independent random width about its average value. The cluster approximation of Niemeyer and Van Leeuwen indicates that the two-dimensional Ising model has the same critical behavior as the homogeneous system. The e expansion for n-component continuous spins shows that this behavior holds to first order in e for n>4. For n<4, there is a new stable fixed point with 2ν=1+[3n/16(n−1)]e.
141 citations
TL;DR: In this paper, a series of amorphous calcium phosphate and hydroxyapatite samples synthesized under different preparative conditions were studied by the x-ray radial distribution method.
139 citations
TL;DR: In this paper, a new method is developed to study the electronic density of states of infinite networks of atoms, which involves treating part of the system exactly as a cluster and simulating the effects of the rest of the environment by connecting a Bethe lattice (Cayley tree) to the surface of the cluster.
Abstract: A new method is developed to study the electronic density of states of infinite networks of atoms. The method involves treating part of the system exactly as a cluster and simulating the effects of the rest of the environment by connecting a Bethe lattice (Cayley tree) to the surface of the cluster. Calculations show that the local ringlike topologies of each atom are of primary importance in determining structure in the electronic density of states. The densities of states of the diamond, BC-8, and ST-12 structures are studied in detail using this method. These calculations are in excellent agreement with the exact results. Because of this, the method is used to obtain the density of states of the Polk and Connell random-network models. These models give the same radial distribution functions but exhibit striking differences in their densities of states which are interpreted in terms of topology.
102 citations
94 citations
TL;DR: In this paper, the results of a systematic study of the size distributions of gold clusters deposited onto NaCl single-crystal surfaces in UHV are presented. But the results are mainly interpreted in terms of a rate equation approach recently given by J.A. Venables.
77 citations
TL;DR: In this paper, Dyson's equation is used to embed an adsorbate/absorbent cluster in the surface of the semi-infinite adsorbent, which is formulated correctly, but to have a practical scheme, an approximate version is needed.
Abstract: To overcome the limitation of conventional quantum chemistry computer programs using the Hartree-Fock approximation which can only handle small clusters of atoms, Dyson's equation is used to embed an adsorbate/absorbent cluster in the surface of the semi-infinite adsorbent. The embedding problem is formulated correctly, but to have a practical scheme, an approximate version is needed. This version uses a tight-binding electron Green function in the adsorbent beyond the cluster, but the correct self-consistent Green function in the adsorbate/adsorbent cluster. Calculations have been made for hydrogen on the (100) surfaces of two simple, and two face-centred cubic s band solids.
TL;DR: In this article, CNDO molecular orbital calculations for nickel atom clusters containing from one to thirteen atoms in various geometric arrangements are presented, and the parameters were selected so that an octahedral Ni6 cluster had an equilibrium inter-nuclear distance, d band occupancy, binding energy, Fermi level, and d band width approximating those of bulk nickel.
TL;DR: In this article, the angular distributions of the average sizes, the velocities, and the molecular intensities of the reflected cluster beams are analyzed for high and low-temperature reflection of clusters.
Abstract: Clusters of helium, hydrogen, and nitrogen are reflected at a polished stainless steel plate at temperatures ranging from 80 to 550 K. The incident clusters contain on the average about 1.5×105 atoms of helium or molecules of hydrogen or 104 molecules of nitrogen, as measured by time‐of‐flight mass spectrometry. The angular distributions of the average sizes, the velocities, and the molecular intensities of the reflected cluster beams show that in the investigated range of reflector temperatures the reflection of the helium clusters corresponds to the hydrogen cluster reflection at higher reflector temperatures while the nitrogen cluster reflection corresponds to the hydrogen cluster reflection at lower reflector temperatures. The transition between the two regimes of reflection as observed with hydrogen clusters is marked by an optimum reflector temperature leading to a maximum intensity of the reflected beam, a minimum loss of clustered material, and a distinct angular separation of incident cluster sizes. At a grazing incidence angle of 84.3° the measured optimum reflector temperature for the hydrogen cluster reflection is 215 K and increases with decreasing angle of incidence. The two regimes of high‐temperature and low‐temperature reflection of clusters exhibit close phenomenological relationship to the regimes of thermal and structure dominated scattering of atoms from single crystal planes. In both cases the transition region is characterized by a maximum angle of reflection and a minimum divergence of the reflected beam. The features of high‐temperature cluster reflection are explained by a semiempirical model based on the evaporation recoil of the cluster molecules ablating after contact with the comparatively hot reflector surface.
TL;DR: In this article, a critique of the traditional Hartree-Fock molecular orbital approach to chemisorption is presented, along with a discussion of recent semi-empirical “LCAO” calculations for graphite.
Abstract: The electronic structures of small clusters of atoms at solid interfaces and of polyatomic aggregates in supporting materials are of central importance to chemisorption and catalysis. Self-consistent field (SCF) molecular orbital theory provides a conceptually simple approach to cluster bonding, but it is of quantitative significance to chemisorption and catalysis only if accurate numerical applications to real systems are practical. A critique of the traditional Hartree-Fock molecular orbital approach to chemisorption is presented, along with a discussion of recent semiempirical “LCAO” calculations for chemisorption on graphite. The recently developed SCF-Xa “scattered-wave” method allows one to calculate highly accurate ground and excited electronic states of polyatomic clusters (as functions of cluster size, composition, geometry, and supporting environment), yet requires only moderate amounts of computer time. Current applications of this technique to chemisorption at transition-metal interfaces and t...
TL;DR: In this article, a theoretical model is proposed suggesting that the unique structural features of the UPS data for oxygen moderately to heavily chemisorbed on nickel are evidence for the incipient formation of surface nickel oxide.
TL;DR: In this article, the title compound was solved by packing considerations and was refined to R 11·9% for the 1584 independent nonzero reflections, with a= 10·098(15), b= 18·788(20), c= 36·712(36)A, and Z= 8.
Abstract: The title compound crystallizes in the centrosymmetric orthorhombic space group Pnma, with a= 10·098(15), b= 18·788(20), c= 36·712(36)A, and Z= 8. The structure was solved by packing considerations and was refined to R 11·9% for the 1584 independent nonzero reflections. The asymmetric unit consists of two half-anions of [Fe6(CO)16C]2–(the remaining halves being generated by crystallographic mirror planes) and two [Me4N]+ cations. The [Fe6(CO)16C]2– anion has 13 terminal carbonyl ligands [two per iron atom, except for Fe(4) which bears three], and 3 ‘semi-bridging’ carbonyls. Nonbridged Fe–Fe bonds range from 2·646(10) to 2·743(10)A, bridged Fe–Fe bonds from 2·553(10) to 2·632(10)A. The encapsulated carbido-carbon atom is octahedrally co-ordinated to six iron atoms, with individual Fe–C distances from 1·805(38) to 1·968(38)A.
TL;DR: In this paper, the canonical partition function was evaluated for clusters having from 6 to 64 water molecules and the intermolecular vibrational free energies were extrapolated to clusters containing up to 120 molecules and free energies of formation, nucleation rates, and critical supersaturation ratios were calculated and compared with experiment.
Abstract: A molecular model previously applied to prenucleation water clusters is used to examine ice Ih embryos. The canonical partition function is evaluated for clusters having from 6 to 64 water molecules. The intermolecular vibrational free energies are extrapolated to clusters containing up to 120 molecules and free energies of formation, nucleation rates, and critical supersaturation ratios are calculated and compared with experiment. For the clusters studied, the ice Ih structure appears to be much less stable at all temperatures than the more spherical clathratelike cluster.
TL;DR: In a previous paper as mentioned in this paper, we discussed the strong decrease properties of the truncated correlation functions, taking into account the separation of all particles with respect to each other, and discussed the effect of the separation on the performance of the correlation functions.
Abstract: In a previous paper, “strong” decrease properties of the truncated correlation functions, taking into account the separation of all particles with respect to each other, have been presented and discussed.
TL;DR: In this paper, small (18-32 atoms) periodic clusters of two-dimensional hexagonal graphite and boron nitride are shown to represent high-symmetry points in the Brillouin zone of the infinite crystal.
Abstract: Small (18-32 atoms) periodic clusters of two-dimensional hexagonal graphite and boron nitride are shown to represent some high-symmetry points in the Brillouin zone of the infinite crystal Semi-empirical all-valence electron calculations are performed on these clusters and the binding energy, work function, bandwidth, band-to-band transition energy, band gap, charges and equilibrium distances are computed and compared with values obtained by tight binding and truncated crystal calculations Favourable agreement with experimental data is obtained with selfconsistent calculations on these clusters
TL;DR: In this paper, a model for spin glasses is proposed in which spins whose RKKY interactions exceed thermal energies define magnetic clusters, and the model predicts Blandin-Souletie scaling at all temperatures and a T-1 specific heat tail.
Abstract: A model for spin glasses is proposed in which spins whose RKKY interactions exceed thermal energies define magnetic clusters. Percolation theory determines the spin glass temperature Tg below which an infinite cluster forms. With suitable anisotropy assumptions the infinite cluster will be superparamagnetically blocked, giving a cusped susceptibility at Tg. A collinear distribution in each cluster gives an effectively one-dimensional internal field at low temperatures. The model predicts Blandin-Souletie scaling at all temperatures and a T-1 specific heat tail.
TL;DR: In this article, the synthesis of carbido-carbonyl clusters has been extended to cobalt for which the anion [Co6(CO)15C]2 has been obtained.
Abstract: New carbido-carbonyl cluster compounds of rhodium have been isolated and two of them, characterized by crystallographic methods, have been formulated as Rh8(CO)19C and [H3O][Rh15(CO)28C2]; the synthesis of carbido-carbonyl clusters has been extended to cobalt for which the anion [Co6(CO)15C]2– has been obtained.
TL;DR: Toxvaerd's extension of the Barker-Henderson perturbation theory to a nonuniform fluid was used to calculate the total free energy of clusters of Lennard-Jones 12−6 atoms as mentioned in this paper.
Abstract: Toxvaerd's extension of the Barker‐Henderson perturbation theory to a nonuniform fluid is used to calculate the total free energy of clusters of Lennard‐Jones 12–6 atoms. The theory predicts a minimum free energy density profile for two chosen cluster sizes, 43‐atoms and 87‐atoms, and the free energy values and profiles agree very well with recent Monte Carlo experiments for such clusters.