Search results for "Hexagonal lattice"
showing 10 items of 37 documents
Fine Grained Tensor Network Methods.
2020
We develop a strategy for tensor network algorithms that allows to deal very efficiently with lattices of high connectivity. The basic idea is to fine-grain the physical degrees of freedom, i.e., decompose them into more fundamental units which, after a suitable coarse-graining, provide the original ones. Thanks to this procedure, the original lattice with high connectivity is transformed by an isometry into a simpler structure, which is easier to simulate via usual tensor network methods. In particular this enables the use of standard schemes to contract infinite 2d tensor networks - such as Corner Transfer Matrix Renormalization schemes - which are more involved on complex lattice structu…
NbxRu6-xTe8, New Chevrel-Type Clusters Containing Niobium and Ruthenium,
1996
Phases of composition Nb(x)()Ru(6)(-)(x)()Te(8) were prepared by reacting stoichiometric mixtures of the elements at high temperature in evacuated silica ampules. The structure of Nb(3.33)Ru(2.67)Te(8) was refined from X-ray powder data using the Rietveld method. Nb(3.33)Ru(2.67)Te(8) crystallizes isotypic with Mo(6)Q(8) (Q = S, Se, Te) in the rhombohedral space group Rthremacr; with the hexagonal lattice parameters a = 10.34106(5) Å, c = 11.47953(7) Å, and Z = 3. Its structure consists of M(6)Te(8) mixed-metal clusters (M = Nb, Ru) which are connected by intercluster M-Te bonds to form a three-dimensional network. Metal-metal bonding in these phases is analyzed in terms of Pauling bond ord…
A new microporous 12-ring zincosilicate THK-2 with many terminal silanols characterized by automated electron diffraction tomography.
2020
A newly synthesized microporous zincosilicate THK-2 (estimated structural composition: |(H2O)6.7(C6H13N)0.9|[Li0.5Zn3.1Si32O62.7(OH)9.3]) was characterized by single-crystal electron diffraction using the automated electron diffraction tomography (ADT) approach in combination with powder X-ray diffraction. The lattice constants and space group of as-synthesized THK-2 were a = 2.50377(7) nm, b = 1.43866(4) nm, c = 0.505369(8) nm, and Pccn (no. 56) with orthorhombic symmetry. Because the crystal lattice was almost identical to a hexagonal lattice (), the first several peaks in its powder X-ray diffraction data severely overlapped, which suppressed the structural information to decide the fram…
Änderungen der Gitterstruktur hochpolymerer Einkristalle durch Bestrahlung im Elektronenmikroskop
1965
Die durch Bestrahlung mit Elektronen von 40 bis 80 kV hervorgerufenen Anderungen der Gitterstruktur von Polyathylen(PA)- und Polyoxymethylen(POM)-Einkristallen wurden unterrsucht. Dazu wurden Lage, Intensitat und Linienbreite der Reflexe im Elektronenbeugungsdiagramm in Abhangigkeit von der Bestrahlungsdosis gemessen. Vergleichende Untersuchungen wurden an einem Paraffin (C28H58) durchgefuhrt. Aus den Anderungen der Linienbreite konnte geschlossen werden, das im Falle des PA durch die Vernetzung zwischen benachbarten Ketten Gitterstorungen II. Art (parakristalline Storungen) hervorgerufen werden. Sie fuhren auch zu einer betrachtlichen Aufewitung des Gitters. Im Falle des Paraffins dagegen …
On the Ground State Structure of Adsorbed Monolayers: Can One Find them by Monte Carlo Simulation?
2002
While the classical ground state structure of an atomic monolayer adsorbed at a noncorrugated perfectly flat substrate trivially is a triangular lattice, the spacing being the minimum of the interatomic potential, nontrivial structures occur on corrugated substrates. This problem is exemplified for the (100) face of a face-centered cubic crystal, varying both the density of the adsorbed monolayer and the strength of the potential due to the surface. Increasing the density beyond that of the commensurate c(2 x 2) structure, incommensurate patterns become stable with “heavy” walls (HW) oriented along the face diagonals [including the “crossing heavy walls” (CRHW) phase]. It is shown that slow…
Phase diagram of a mixed polymer brush
2001
We investigate the structure and phase behavior of a two-component (binary) polymer brush in a solvent within self-consistent field theory as a function of the chains' stretching, the composition, and the incompatibility. Grafting the chains irreversibly prevents macrophase separation and the chains assemble into three-dimensional structures with lateral periodicity. At small incompatibilities a "ripple" phase is formed where different species aggregate into an array of parallel cylinders. At larger incompatibilities or asymmetric composition two "dimple" phases become stable, where different species form clusters which arrange on a quadratic (checkerboard structure) or hexagonal lattice.
From dewetting to wetting molecular layers: C60 on CaCO3(10 ̅14) as a case study.
2012
We report the formation of extended molecular layers of C-60 molecules on a dielectric surface at room temperature. In sharp contrast to previous C-60 adsorption studies on prototypical ionic crystal surfaces, a wetting layer is obtained when choosing the calcite (CaCO3)(10 (1) over bar4) surface as a substrate. Non-contact atomic force microscopy data reveal an excellent match of the hexagonal lattice of the molecular layer with the unit cell dimension of CaCO3(10 (1) over bar4) in the [01 (1) over bar0] direction, while a lattice mismatch along the [(4) over bar(2) over bar 61] direction results in a large-scale moire modulation. Overall, a (2 x 15) wetting layer is obtained. The distinct…
Chalcogenide glass hollow core photonic crystal fibers
2010
International audience; We report the first hollow core photonic crystal fibers (HC PCF) in chalcogenide glass. To design the required HC PCF profiles for such high index glass, we use both band diagram analysis to define the required photonic bandgap and numerical simulations of finite size HC PCFs to compute the guiding losses. The material losses have also been taken into account to compute the overall losses of the HC PCF profiles. These fibers were fabricated by the stack and draw technique from Te20As30Se50 (TAS) glass. The fibers we drew in this work are composed of six rings of holes and regular microstructures. Two profiles are presented, one is known as a kagome lattice and the ot…
Motion, relaxation dynamics, and diffusion processes in two-dimensional colloidal crystals confined between walls
2012
The dynamical behavior of single-component two-dimensional colloidal crystals confined in a slit geometry is studied by Langevin dynamics simulation of a simple model. The colloids are modeled as pointlike particles, interacting with the repulsive part of the Lennard-Jones potential, and the fluid molecules in the colloidal suspension are not explicitly considered. Considering a crystalline strip of triangular lattice structure with n=30 rows, the (one-dimensional) walls confining the strip are chosen as two rigidly fixed crystalline rows at each side, commensurate with the lattice structure and, thus, stabilizing long-range order. The case when the spacing between the walls is incommensura…
Two-dimensional mobile breather scattering in a hexagonal crystal lattice.
2021
We describe the full two-dimensional scattering of long-lived breathers in a model hexagonal lattice of atoms. The chosen system, representing an idealized model of mica, combines a Lennard-Jones interatomic potential with an “egg-box” harmonic potential well surface. We investigate the dependence of breather properties on the ratio of the well depths associated with the interaction and on-site potentials. High values of this ratio lead to large spatial displacements in adjacent chains of atoms and thus enhance the two-dimensional character of the quasi-one-dimensional breather solutions. This effect is further investigated during breather-breather collisions by following the constrained en…