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Michael P Allen

Publications and source records attributed to Michael P Allen.

10 recordsLinked to original sources
PubMed2006

Structure of a liquid crystalline fluid around a macroparticle: Density functional theory.

The structure of a molecular liquid, in both the nematic liquid crystalline and isotropic phases, around a cylindrical macroparticle, is studied using density functional theory. In the nematic phase the structure of the fluid is highly anisotropic with respect to the director, in agreement with results from simulation and phenomenological theories. On going into the isotropic phase the structure becomes rotationally invariant around the macroparticle with an oriented layer at the surface.

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PubMed2006

Structure of molecular liquids: cavity and bridge functions of the hard spheroid fluid.

We present methodologies for calculating the direct correlation function c(1,2), the cavity function y(1,2), and the bridge function b(1,2), for molecular liquids, from Monte Carlo simulations. As an example we present results for the isotropic hard spheroid fluid with elongation e = 3. The simulation data are compared with the results from integral equation theory. In particular, we solve the Percus-Yevick and hypernetted chain equations. In addition, we calculate the first two terms in the virial expansion of the bridge function and incorporate this into the closure. At low densities, the bridge functions calculated by theory and from simulation are in good agreement, lending support to the correctness of our numerical procedures. At higher densities, the hypernetted chain results are brought into closer agreement with simulation by incorporating the approximate bridge function, but significant discrepancies remain.

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PubMed2006

Evaluation of pressure tensor in constant-volume simulations of hard and soft convex bodies.

A method for calculating the pressure tensor in constant-volume Monte Carlo simulations of convex bodies is presented. In contrast to other approaches, the method requires only an isotropic scaling of the simulation box and the counting of simple geometric quantities characterizing overlapping pairs. Nonsphericity presents no special difficulties. The result is expressed as a sum of pairwise contributions and can therefore be used to compute pressure tensor profiles in a conventional way.

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PubMed2006

Configurational temperature in membrane simulations using dissipative particle dynamics.

The use of excessively long time steps in dissipative particle dynamics simulations may produce simulation artifacts due to the generation of configurations which are not representative of the desired canonical ensemble. The configurational temperature, among other quantities, may be used to assess the extent of the deviation from equilibrium. This paper presents results for simulations of models of water and lipid bilayer membranes to illustrate the nature of the problems.

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PubMed2005

Spin dynamics for the Lebwohl-Lasher model.

A spin dynamics algorithm, combining checkerboard updating and a rotation algorithm based on the local second-rank ordering field, is developed for the Lebwohl-Lasher model of liquid crystals. The method is shown to conserve energy well and to generate simulation averages that are consistent with those obtained by Monte Carlo simulation. However, care must be taken to avoid the undesirable effects of director rotation, and a method for doing this is proposed.

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PubMed2002

Defect structures and torque on an elongated colloidal particle immersed in a liquid crystal host.

Combining molecular dynamics and Monte Carlo simulation, we study defect structures around an elongated colloidal particle embedded in a nematic liquid crystal host. By studying nematic ordering near the particle and the disclination core region, we are able to examine the defect core structure and the difference between two simulation techniques. In addition, we also study the torque on a particle tilted with respect to the director, and modification of this torque when the particle is close to the cell wall.

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PubMed2002

Theory and simulation of the nematic zenithal anchoring coefficient.

Combining molecular simulation, Onsager theory, and the elastic description of nematic liquid crystals, we study the dependence of the nematic liquid crystal elastic constants and the zenithal surface anchoring coefficient on the value of the bulk order parameter.

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