Cubic Lattice (cubic + lattice)

Distribution by Scientific Domains

Selected Abstracts

Architecture of Polymeric Superstructures Constructed by Mesoscopically Ordered Cubic Lattices

Koji Ishizu
Abstract Highly monodisperse crosslinked core-shell polymer microspheres could be prepared easily by introducing special crosslinking reagents into the segregated core in block copolymer assembly films. The crosslinked core was stabilized sterically by highly branched shell chains in solution. These microspheres moved like pseudo-latex. The microspheres formed a lattice with a body-centered cubic (BCC) structure near the overlap threshold (C*). This structure changed to a face-centered cubic (FCC) lattice in the bulk region of the films. Photofunctionalized core-shell microspheres were prepared by introducing dithiocarbamate (DC) groups into shell parts by means of polymer reactions, where DC groups could be propagated using vinyl monomers such as methyl methacrylate (MMA) with living radical mechanism. Polymeric superstructure (three microphase-separated structure) films were constructed by graft copolymerization of MMA initiated with photofunctionalized microspheres such as macroinitiators under UV irradiation, exhibiting self-coloring due to Bragg diffraction. These materials can be used for the construction of optical devices such as for the fabrication of light modulators. Photograph of a solution of the microsphere in MMA. [source]

Electrostatic energies and forces computed without explicit interparticle interactions: A linear time complexity formulation

Robert J. Petrella
Abstract A rapid method for the calculation of the electrostatic energy of a system without a cutoff is described in which the computational time grows linearly with the number of particles or charges. The inverse of the distance is approximated as a polynomial, which is then transformed into a function whose terms involve individual particles, instead of particle pairs, by a partitioning of the double sum. In this way, the electrostatic energy that is determined by the interparticle interactions is obtained without explicit calculation of these interactions. For systems of positive charges positioned on a face-centered cubic lattice, the calculation of the energy by the new method is shown to be faster than the calculation of the exact energy, in many cases by an order of magnitude, and to be accurate to within 1,2%. The application of this method to increase the accuracy of conventional truncation-based calculations in condensed-phase systems is also demonstrated by combining the approximated long-range electrostatic interactions with the exact short-range interactions in a "hybrid" calculation. For a 20-Å sphere of water molecules, the forces are shown to be six times as accurate using this hybrid method as those calculated with conventional truncation of the electrostatic energy function at 12 Å. This is accomplished with a slight increase in speed, and with a sevenfold increase in speed relative to the exact all-pair calculation. Structures minimized with the hybrid function are shown to be closer to structures minimized with an exact all-pair electrostatic energy function than are those minimized with a conventional 13-Å cutoff-based electrostatic energy function. Comparison of the energies and forces calculated with the exact method illustrate that the absolute errors obtained with standard truncation can be very large. The extension of the current method to other pairwise functions as well as to multibody functions, is described. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 755,787, 2005 [source]

Monte-Carlo Study of Triblock Copolymer/Homopolymer Blend Films

Yongmin Huang
Abstract The morphologies of triblock copolymer/homopolymer blend films confined between two neutral hard walls were studied via MC simulations on a simple cubic lattice. For ABA/A and ABA/B blend films, the effects of ,h (the volume fraction of the homopolymer) and Mh/Mb (the ratio of the molecular mass of the homopolymer to that of the corresponding blocks) on the morphologies were investigated in detail. For both ABA/A and ABA/B blend films, a higher ,h or Mh/Mb would result in stronger macrophase separation between the triblock copolymer and homopolymer. For ABA/C blend films, Mh/Mb hardly influences the morphologies of homopolymer domains regardless of whether the homopolymer C is more compatible with block A or with block B. Compared to AB/A and AB/C blend films, the morphologies of ABA/A (or ABA/B) and ABA/C blend films are much more irregular. The simulated results in this work show good consistency with experiments and other simulations. [source]

Monte Carlo Simulations of the Morphologies and Conformations of Triblock Copolymer Thin Films

Yongmin Huang
Abstract Summary: The morphologies and conformations of triblock copolymer (ABA and ABC) thin films confined between two identical walls were investigated by Monte Carlo simulation using bond length fluctuation and cavity diffusion algorithm on cubic lattice. Effects of the wall-block interactions, copolymer chain composition and film thickness on morphologies, as well as on the fraction of chain "bridge" conformation fbridge are presented in detail. In ABA thin film, column, parallel, perforated and perpendicular lamellas were discriminated, furthermore, the transition of morphology and the variation of fbridge of ABA film along with the increase of thickness were revealed. In ABC thin film, lamella especially perpendicular lamella morphologies are predominant in varying the wall-block interactions and the thickness. The results are consistent with some theoretical predictions such as DDFT and simulations reported in literature. Isodensity profile of A5B5A5 thin film. [source]

Phase diagram of a thin Heisenberg antiferromagnetic film

J. Cabral Neto
Abstract We investigate the thickness dependence of the Néel temperature of a thin quantum spin-1/2 Heisenberg antiferromagnetic film as a function of the magnetic field on a simple cubic lattice. The Néel temperature TN(H, ,) is obtained by using the framework of the effective-field theory for films consisting of , = 2, 3, 5, 10 and , (bulk) interacting layers. We present the phase diagram of T versus H in the whole range of the magnetic field for several values of ,. A continuous phase-transition line separating the antiferromagnetic and ferromagnetic phases is observed. The critical temperature TN(H, ,) of the film is smaller than the corresponding bulk critical temperature (H) , TN(H, ,) of the infinite system, which has been analyzed recently by Bublitz Filho and de Sousa [Phys. Lett. A 323, 9 (2004)]; as , is increased, TN(H, ,) also increases and approaches (H) for large values of ,. We have, also, studied the quantum phase transition where three critical fields were found: Hc(,) = 6.224 for , , 3 (three-dimensional regime), Hc(, = 2) = 5.210 (intermediate regime) for , = 2 and, finally, the two-dimensional regime at , = 1 with Hc(, = 1) = 4.194. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Monte Carlo Simulations of the 3D Ashkin,Teller Model: continuous phase transition lines

G. Musia
Abstract Large-scale Monte Carlo simulations, based on the invariance of the Binder cumulant Q, for continuous phase transitions in the three-dimensional Ashkin,Teller spin-lattice model on a cubic lattice, have been performed. Using the universality hypotesis and the finite-size-scaling analysis, the Ising character of phase transitions from the antiferro- to paramagnetic phase, where the cumulant Q behavior is different than in the Ising model, is demonstrated. Some preliminary results demonstrating the existance of the tricritical points are also presented. [source]

Jahn-Teller distortions and off centre motions in impurities: Microscopic insight

P. García-Fernández
Abstract Ab intio calculations are shown to play an important role for clarifying the mechanisms responsible for Jahn-Teller and off-centre distortions induced by transition-metal impurities in insulating materials. Examples concerning a d7 impurity in a cubic lattice, d9 impurities in tetragonal perovskites with K2NiF4 structure and Cu2+ and Ni+ ions in lattices with fluorite structure are discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Potassium yttrium hexaniobium octadecachloride, KYNb6Cl18

Thirumalai Duraisamy
The structure of potassium yttrium hexaniobium octadeca­chloride is built of anionic [Nb6Cl12iCl6a]4, cluster units (where `i' and `a' denote inner and outer ligands, respectively), linked together by K+ and Y3+ cations. The K+ cations occupy half of the tetrahedral vacancies in the face-centered cubic lattice of cluster units, and are coordinated by 12 chloride ligands. The Y atom is located in an octahedral site and is bonded to six outer chloride ligands. [source]

Ion,Dipole Interactions in Concentrated Organic Electrolytes

CHEMPHYSCHEM, Issue 6 2003
Alexandre Chagnes
Abstract An algorithm is proposed for calculating the energy of ion,dipole interactions in concentrated organic electrolytes. The ion,dipole interactions increase with increasing salt concentration and must be taken into account when the activation energy for the conductivity is calculated. In this case, the contribution of ion,dipole interactions to the activation energy for this transport process is of the same order of magnitude as the contribution of ion,ion interactions. The ion,dipole interaction energy was calculated for a cell of eight ions, alternatingly anions and cations, placed on the vertices of an expanded cubic lattice whose parameter is related to the mean interionic distance (pseudolattice theory). The solvent dipoles were introduced randomly into the cell by assuming a randomness compacity of 0.58. The energy of the dipole assembly in the cell was minimized by using a Newton,Raphson numerical method. The dielectric field gradient around ions was taken into account by a distance parameter and a dielectric constant of ,=3 at the surfaces of the ions. A fair agreement between experimental and calculated activation energy has been found for systems composed of ,-butyrolactone (BL) as solvent and lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) as salts. [source]