Eight-point density correlation functions in lennard-jones fluids

Molecular dynamics calculations of components of the eight-point four-time density correlation function around a probe mulecule in a Lennard-Jones host fluid have been made. This function has important consequences for the interpretation of line broadening and other collision-induced spectroscopic experiments.     

Atomic wave functions for the configurations snpm studied by the projection operator technique

Tables of angular momentum wave functions and energy matrices for the atomic configurations s ⁿ p^m are given in the cases of strong, weak and intermediate coupling. Also the transformation matrices between LS- and jj-coupling are calculated.All these calculations are carried out as an application of the projection operator method for angular momenta, introduced by Löwdin.

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Zusammenfassung Eigenfunktionen des Drehimpulses und entsprechende Energiematrizen für die Atomkonfigurationen s ⁿ p^m sind für die drei Kopplungsfälle, LS, jj und intermediär tabelliert. Matrizen für Transformationen zwischen LS- und jj-Kopplung werden angegeben. Alle diese Rechnungen sind auf die von Löwdin eingeführte Projektionsoperatormethode gegründet.

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Résumé On a calculé des fonctions propres du moment cinétique ainsi que les matrices correspondantes de l'énergie, pour les configurations atomiques s ⁿ p^m. Les trois types de couplage, LS, jj et intermédiaire ont été étudiés, ainsi que les matrices de transformation entre ces couplages. Pour tous ces calculs on a utilisé la méthode des projecteurs pour le moment cinétique, introduite par Löwdin.

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A preliminary version of this paper was published as a Technical Note No. 39 from the Quantum Chemistry Group, University of Uppsala, March 1, 1960.The work reported in this paper has been sponsored in part by the King Gustaf VI Adolf's 70-Year Fund for Swedish Culture, Knut and Alice Wallenberg's Foundation, the Swedish Natural Science Research Council, and in part by the Aeronautical Research Laboratory Wright Air Development Division of the Air Research and Development Command, United States Air Force, through its European Office.     

Molecular dynamics study of A18B lennard-jones clusters

Low temperature structures, melting and evaporation temperatures of A₁₈B clusters with Lennard-Jones interactions have been studied using Molecular Dynamics simulations for different values of the parameters representing (a) the size ratio between A and B atoms, and (b) the ratio between the strengths of the A - B and A - A interactions.This paper was originally submitted in connection with the 2nd. Int. Conference on Atoic and Nuclear Clusters held in Santorini from 28. June–2. July 1993 and is published here as a regular article after an independent refereeing procedure according to the standards of Z. Phys. D     

Molecular relaxation processes in the salt systems containing anions of various configurations

We present in this paper a comparative analysis of the spectral and molecular-relaxation parameters of the ionic salts in the region of solid-liquid phase transition and in the molten state depending on the anion symmetry (thiocyanate (SCN-), a linear rotor, C(infinity v); nitrate (NO3-), a symmetrical top, D3h; and perrhenate (ReO4-), a spherical top, Td), size and charge of the cation, and temperature. We also present new results of the investigations on molecular relaxation in thiocyanate ion in several crown-etheric complexes.     

Stabilization of hexagonal close-packed metallic nickel for alumina-supported systems prepared from Ni(II) glycinate

The decomposition in flowing argon of the neutral complex [Ni^II(glycinate)₂(H₂O)₂] leads to a mixture of face-centered cubic (fcc) and hexagonal close-packed (hcp) metallic nickel. The latter is the main phase when the Ni(II) complex is supported on alumina. Unlike most hexagonal Ni phases described earlier, and similar to hexagonal Ni₃C, the unit cell parameters (a=0.2493 and ) lead to Ni-Ni distances equal to those encountered in fcc Ni. TEM shows that the nanoparticles are protected by graphite layers, whose elimination by heating in hydrogen results in transformation to the fcc phase and crystal growth. Magnetic measurements provide evidence of the coexistence of superparamagnetic and ferromagnetic nanoparticles. This result is in line with the broad size distribution observed by TEM and is interpreted on the basis of the metallic character of hcp Ni particles.     

A simple lennard-jones model for computer simulation of conformational disordering in polymers

A simple generalized model is proposed to describe the phenomenon of conformational disordering in polymers. The model represents a two-dimensional system of flexible particles interacting through a modified Lennard-Jones potential. Monte Carlo simulation of the phase behavior of the model system shows that the model is quite adequate to describe all essential features inherent in the transition to the conformationally disordered state.     

The combinatorics of cation-deficient close-packed structures

Pólya's enumeration theorem is used to derive an algorithm for counting all hexagonal close-packed structures with a unit cell of given size, having composition MX₂, where X is an hcp anion, M is an octahedrally coordinated cation, and no face sharing is permitted between octahedra. Generalizations of this algorithm to enumerate ordered derivatives of these structures, hcp structures with tetrahedral instead of octahedral cations, and similar structures having different stacking sequences among the close-packed layers are sketched.     

Water wettability of close-packed metal surfaces

We propose a new microscopic criterion to determine surface wetting: water wets the surface whenever its overlayer has a larger adsorption energy than three-dimensional clusters on the bare or water-covered substrate. This conceptually intuitive criterion is validated by detailed first-principles calculations of the energetics of layers and clusters of water on different metal surfaces. This criterion resolves naturally the current discrepancy between theory and experiment on the wetting behavior of undissociated water on Ru(0001), as well as the hydrophobic nature of the Au(111) surface. It also explains the Stranski-Krastanov ice growth on Pt(111) observed experimentally.     

Clever and efficient method for searching optimal geometries of lennard-jones clusters

An unbiased algorithm for determining global minima of Lennard-Jones (LJ) clusters is proposed in the present study. In the algorithm, a global minimum is searched by using two operators: one modifies a cluster configuration by moving atoms to the most stable positions on the surface of a cluster and the other gives a perturbation on a cluster configuration by moving atoms near the center of mass of a cluster. The moved atoms are selected by employing contribution of the atoms to the potential energy of a cluster. It was possible to find new global minima for LJ506, LJ521, LJ536, LJ537, LJ538, and LJ541 together with putative global minima of LJ clusters of 10-561 atoms reported in the literature. This indicates that the present method is clever and efficient for cluster geometry optimization.     

Effect of meniscus geometry on equilibrium pressures of the lennard-jones liquids

The theory of phase transitions on interfaces relates equilibrium vapor pressures and enthalpies of condensation. Since the latter are size- and shape-dependent properties and their variations are determined by variations of energies of autoadsorption on liquid menisci, a knowledge of these energies enable one to calculate the equilibrium pressures in capillaries. The novel mathematical model for a computation of the adsorption energies is developed on the basis of the Lennard-Jones potential for molecular interactions. The model is applied to hemispherical, conical, cylindrical, semi-elliptical, and paraboloidal menisci in nanocapillaries. Predicted equilibrium vapor pressures are favorably compared with the independent experimental data.     

Freezing phenomena of lennard-jones fluid confined in jungle-gym nanospace: a monte carlo study

We performed grand canonical Monte Carlo simulations for a Lennard-Jones fluid confined in a jungle-gym (JG) nanospace of cubic structure modeled on a specific type of metal organic frameworks (MOFs) to investigate freezing phenomena. Our simulations clarified that the JG nanospace with the pore sizes from 5sigma to 11sigma strongly depresses freezing due to a geometrical hindrance effect, resulting in far lower freezing temperature than the bulk freezing point. The fluid-rod interaction is found to give little effect on the freezing temperature in the larger pore sizes. For smaller pores from 2sigma to 3sigma, on the other hand, a dominant factor is a template effect to enhance the localization of molecules into a specific configuration that matches the locations of potential minima, leading to a variety of molecular configurations. In this range of smaller pore sizes, the solidification temperatures are higher than those of the larger pores mainly due to strong influence of the fluid-rod interaction but are still lower than the bulk freezing temperature. In addition, a unique solid-to-solid transition is observed in a specific size of pore of 2.73sigma, which is caused by structural correlation between adjacent cells. On the basis of these results, a phase diagram in the JG nanospace is drawn.     

The classical and quantum-mechanical free energy of solid (lennard-jones) argon

The classical and quantum-mechanical free energies of crystalline (fcc) argon were determined at two state points by classical and path integral Monte Carlo methods. The quantum corrections to the free energy, energy and pressure so obtained are compared with corrections based on the harmonic approximation and the first-order term in the Wigner-Kirkwood expansion.     

Preparation and characterization of hexagonal close-packed Ni nanoparticles

Hexagonal close-packed Ni nanoparticles were synthesized using a heat-treating technique with the precursors prepared by the sol-gel method. The synthesis condition, structure, and morphology of the samples were characterized and analysed by thermogravimetric analysis (TG), differential thermal analysis (DTA), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results indicate that the hexagonal close packed Ni nanoparticles were synthesized at a heat-treating temperature of 300°C. The cell constants are calculated at a = 0.2652 nm and c = 0.4334 nm. The average grain size of the hexagonal close-packed Ni particles evaluated by Scherrer equation is about 12 nm. The phase transformation from a hexagonal close-packed Ni to a face-centered cubic Ni structure occurred when the heat-treating temperature was increased. __________ Translated from Chemical Journal of Chinese Universities, 2007, 28(7): 1232–1234 [译自: 高等学校化学学报]     

High-nuclearity close-packed palladium-nickel carbonyl phosphine clusters: heteropalladium

[Pd(16)Ni(4)(CO)(22)(PPh(3))(4)](2)(-) (1) and [Pd(33)Ni(9)(CO)(41)(PPh(3))(6)](4)(-) (2) were obtained as the two major products from the reduction of PdCl(2)(PPh(3))(2) with [Ni(6)(CO)(12)](2)(-). Their crystal structures as [PPh(4)](+) salts were unambiguously determined from CCD X-ray crystallographic analyses; the resulting stoichiometries were ascertained from elemental analyses. Infrared, multinuclear (1)H, (31)P[(1)H] NMR, UV-vis, CV, variable-temperature magnetic susceptibility, and ESI FT/ICR mass spectrometric measurements were performed. The Pd(16)Ni(4) core of 1 ideally conforms to a ccp nu(3) tetrahedron of pseudo-T(d)() (4 3m) symmetry. Its geometry normal to each tetrahedral Pd(7)Ni(3) face (i.e., along each of the four 3-fold axes) may be viewed as a four-layer stacking of 20 metal atoms in a ccp [a(Ni(1)) b(Pd(3)) c(Pd(6)) a(Pd(7)Ni(3))] sequence. A comparative analysis of the different ligand connectivities about the analogous metal-core geometries in 1 and the previously reported [Os(20)(CO)(40)](2)(-) has stereochemical implications pertaining to the different possible modes of carbon monoxide attachment to ccp metal(111) surfaces. The unique geometry of the Pd(33)Ni(9) core of 2, which has pseudo-D(3)(h)() (6 2m) symmetry, consists of five equilateral triangular layers that are stacked in a hcp [a(Pd(7)Ni(3)) b(Pd(6)) a(Pd(7)Ni(3)) b(Pd(6)) a(Pd(7)Ni(3))] sequence. Variable-temperature magnetic susceptibility measurements indicated both 1 and 2 to be diamagnetic over the entire temperature range from 5.0 to 300 K. Neutral Pd(12)(CO)(12)(PPh(3))(6) (3) and [Pd(29)(CO)(28)(PPh(3))(7)](2)(-) (4) as the [PPh(4)](+) salt were obtained as minor decomposition products from protonation reactions of 1 and 2, respectively, with acetic acid. Compound 3 of pseudo-D(3)(d)() (3 2/m) symmetry represents the second highly deformed hexacapped octahedral member of the previously established homopalladium family of clusters containing uncapped, monocapped, bicapped, and tetracapped Pd(6) octahedra. The unprecedented centered 28-atom polyhedron for the Pd(29) core of 4 of pseudo-C(3)(v)() (3m) symmetry may be described as a four-layer stacking of 29 metal atoms in a mixed hcp/ccp [a(Pd(1)) b(Pd(3)) a(Pd(10)) c(Pd(15))] sequence.     

The generic geometry of helices and their close-packed structures

The formation of helices is an ubiquitous phenomenon for molecular structures whether they are biological, organic, or inorganic, in nature. Helical structures have geometrical constraints analogous to close-packing of three-dimensional crystal structures. For helical packing the geometrical constraints involve parameters such as the radius of the helical cylinder, the helical pitch angle, and the helical tube radius. In this communication, the geometrical constraints for single helix, double helix, and for double helices with minor and major grooves are calculated. The results are compared with values from the literature for helical polypeptide backbone structures, the α-, π-, 3₁₀-, and γ-helices. The α-helices are close to being optimally packed in the sense of efficient use of space, i.e. close-packed. They are also more densely packed than the other three types of helices. For double helices comparisons are made to the A, B, and Z forms of DNA. The helical geometry of the A form is nearly close-packed. The packing density for the B and Z forms of DNA are found to be approximately equal to each other.     

Parametric effects of the potential energy function on the geometrical features of ternary lennard-jones clusters

The impact of parameters in potential function for describing atomic or molecular clusters is complex due to the complicated potential energy surface. Ternary Lennard-Jones (TLJ) A(l)B(m)C(n) clusters with two-body potential are investigated to study the effect of parameters. In the potential, the size parameter (σ(AA)) of A atoms is fixed, and corresponding parameters of B and C atoms (relative to A atoms), i.e., σ(BB)/σ(AA) and σ(CC)/σ(AA) > 1.00, are used to control the atomic interaction among A, B, and C atoms in TLJ clusters. The minimum energy configurations of A(l)B(m)C(n) clusters with different species are optimized by adaptive immune optimization algorithm. Ternary cluster structures, bonds, and energies of the putative minima are studied. The results show that two different structures based on double-icosahedra are found in 30-atom TLJ clusters. Furthermore, with increasing potential size parameters of B and C atoms, A atoms tend to be more compact for the increasing numbers of A-A bonds, but the short-range attractive part in TLJ clusters becomes weaker. To lower the potential energy, B and C atoms grow around the A atoms in pursuit of a compact configuration. The results are also approved in A(l)B(m)C(n) (l + m + n = 9-55) clusters and A(l)B(m)C(n) (l = 13, m + n = 42) clusters.