Canonical Ensemble (canonical + ensemble)

Distribution by Scientific Domains
Chemistry75%
Physics and Astronomy25%

Kinds of Canonical Ensemble

  • grand canonical ensemble
    		•

    Selected Abstracts

    Models for the adsorption and self-assembly of ethanol and 1-decanethiol on Au(111) surfaces.

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2010
    A comparative study by computer simulation
    Abstract Results from computer simulations, based on different models to study theadsorption and self-assembly of the ethanol and 1-decanethiol on gold surfaces, Au(111), are presented. Canonical ensemble Monte Carlo simulations were performed at 298 K using two different force fields. One from DFT calculations, where the gold electrode has an explicit structure (corrugated electrode), and the other representing an electrode, in which the structure is taken into account on an average way (flat electrode). The behavior of the ethanol adsorption on gold surfaces, with and without the 1-decanethiol presence, is analyzed. The introduction of molecular flexibility is also discussed. The relative surface density for the ethanol oxygen, adsorbed on gold, and the density profiles, in different conditions, show that the structure of the surface has a fundamental role on the way the adsorption takes place, not only on the preferential adsorption sites of the surface but also on the ethanol distribution over the electrodes. Potentials of mean force have also been calculated for the two surface models, giving the free energy barriers to the 1-decanethiol crossing of the solvent adsorption layers. The average tilt angle, obtained with a single thiol molecule in the simulation box, presents the values: ,26° for the rigid molecule model and 74° ± 18° for the flexible one. These differences are analyzed. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source]

    New phases of thermal SYM and LST from Kaluza-Klein black holes

    FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 7-8 2005
    T. Harmark
    Abstract We review the recently found map that takes any static and neutral Kaluza-Klein black hole, i.e. any static and neutral black hole on Minkowski-space times a circle ,d × S1, and maps it to a corresponding solution for a non- and near-extremal brane on a circle. This gives a precise connection between phases of Kaluza-Klein black holes and the thermodynamic behavior of the non-gravitational theories dual to near-extremal branes on a circle. In particular, for the thermodynamics of strongly-coupled supersymmetric Yang-Mills theories on a circle we predict the existence of a new non-uniform phase and find new information about the localized phase. We also find evidence for the existence of a new stable phase of (2,0) Little String Theory in the canonical ensemble for temperatures above its Hagedorn temperature. [source]

    Molecular dynamics simulation in the grand canonical ensemble

    JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 10 2007
    Hossein Eslami
    Abstract An extended system Hamiltonian is proposed to perform molecular dynamics (MD) simulation in the grand canonical ensemble. The Hamiltonian is similar to the one proposed by Lynch and Pettitt (Lynch and Pettitt, J Chem Phys 1997, 107, 8594), which consists of the kinetic and potential energies for real and fractional particles as well as the kinetic and potential energy terms for material and heat reservoirs interacting with the system. We perform a nonlinear scaling of the potential energy parameters of the fractional particle, as well as its mass to vary the number of particles dynamically. On the basis of the equations of motion derived from this Hamiltonian, an algorithm has been proposed for MD simulation at constant chemical potential. The algorithm has been tested for the ideal gas, for the Lennard,Jones fluid over a wide range of temperatures and densities, and for water. The results for the low-density Lennard,Jones fluid are compared with the predictions from a truncated virial equation of state. In the case of the dense Lennard,Jones fluid and water our predicted results are compared with the results reported using other available methods for the calculation of the chemical potential. The method is also applied to the case of vapor-liquid coexistence point predictions. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [source]

    Monte Carlo simulation of adsorption using 2-D models of heterogeneous solids

    AICHE JOURNAL, Issue 3 2003
    V. F. Cabral
    A new methodology proposed here correlates the adsorption of pure components and predicts the adsorption of binary and ternary mixtures in homogeneous and heterogeneous solids. This methodology uses the algorithm of molecular simulation in the grand canonical ensemble as an equation of state for the adsorbed phase. In all case studies presented, the simulations described the adsorption characteristics of systems. The results obtained for the adsorption of the binary mixtures of propane,CO2 and propane,H2S, which are strongly nonideal, were quite satisfactory, showing the potential of this technique for the description of real systems. [source]

    Vapor,liquid equilibria of mixtures containing alkanes, carbon dioxide, and nitrogen

    AICHE JOURNAL, Issue 7 2001
    Jeffrey J. Potoff
    New force fields for carbon dioxide and nitrogen are introduced that quantitatively reproduce the vapor,liquid equilibria (VLE) of the neat systems and their mixtures with alkanes. In addition to the usual VLE calculations for pure CO2 and N2, calculations of the binary mixtures with propane were used in the force-field development to achieve a good balance between dispersive and electrostatic (quadrupole,quadrupole) interactions. The transferability of the force fields was then assessed from calculations of the VLE for the binary mixtures with n-hexane, the binary mixture of CO2/N2, and the ternary mixture of CO2 /N2/propane. The VLE calculations were carried out using configurational-bias Monte Carlo simulations in either the grand canonical ensemble with histogram,reweighting or in the Gibbs ensemble. [source]

    Magnetic impurities in small metal clusters

    ANNALEN DER PHYSIK, Issue 9-10 2005
    G.M. Pastor
    Abstract Magnetic impurities in small metallic clusters are investigated in the framework of the Anderson model by using exact diagonalization and geometry optimization methods. The singlet-triplet spin gap ,E shows a remarkable dependence as a function of band-filling, cluster structure, and impurity position that can be interpreted in terms of the environment-specific conduction-electron spectrum. The low-energy spin excitations involve similar energies as isomerizations. Interesting correlations between cluster structure and magnetic behavior are revealed. Finite-temperature properties such as specific heat, effective impurity moment, and magnetic susceptibility are calculated exactly in the canonical ensemble. A finite-size equivalent of the Kondo effect is identified and its structural dependence is discussed. [source]

    Local Structure and Thermodynamics of a Core-Softened Potential Fluid: Theory and Simulation

    CHEMPHYSCHEM, Issue 1 2007
    Shiqi Zhou Dr.
    Abstract Phase behavior and structural properties of homogeneous and inhomogeneous core-softened (CS) fluid consisting of particles interacting via the potential, which combines the hard-core repulsion and double attractive well interaction, are investigated. The vapour,liquid coexistence curves and critical points for various interaction ranges of the potential are determined by discrete molecular dynamics simulations to provide guidance for the choice of the bulk density and potential parameters for the study of homogeneous and inhomogeneous structures. Spatial correlations in the homogeneous CS system are studied by the Ornstein-Zernike integral equation in combination with the modified hypernetted chain (MHNC) approximation. The local structure of CS fluid subjected to diverse external fields maintaining the equilibrium with the bulk CS fluid are studied on the basis of a recently proposed third order+second order perturbation density functional approximation (DFA). The accuracy of DFA predictions is tested against the results of a grand canonical ensemble Monte Carlo simulation. Reasonable agreement between the results of both methods proves that the DFA theory applied in this work is a convenient theoretical tool for the investigation of the CS fluid, which is practically applicable for modeling numerous real systems. [source]