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A coarser model for the Gay-Berne mesogen is developed using the interaction potential from the Approximate Non-Conformal (ANC) theory. The ANC potential contains both repulsive and attractive contributions. We modify intermolecular attractions by conditioning them with a Hess-Su orientation-dependent term. This imparts an anisotropic contribution to the energy of the system. The softness parameter s of the ANC potential is probed to qualitatively identify a threshold capable of sustaining a nematic phase. We construct phase diagrams for each value of s from molecular dynamics simulations and characterise bulk samples to outline phase regions. We find that a softness parameter $ s \sim 0.6 $ s ∼ 0.6 or higher supports the emergence of a nematic phase. The stability of the nematic region is enhanced as $ s\to 1 $ s → 1 , corresponding to the conventional Lennard-Jones interaction. The stability of the nematic phase for nearly-spherical mesogens with increasing s leads to a gradual loss in spherical symmetry despite no imposed shape anisotropy. Thus, the energy anisotropy becomes more pronounced and is capable of prompting the emergence of the nematic phase in this model. [ABSTRACT FROM AUTHOR]

Starting from the Ornstein-Zernike equation the authors derive an analytical theory, at the level of pair correlation functions, which coarse grains polymer melts into liquids of interacting soft colloidal particles. Since it is analytical, the presented coarse-graining approach will be useful in developing multiscale modeling procedures to simulate complex fluids of macromolecules. The accuracy of the theory is tested by its capacity to reproduce the liquid structure, as given by the center-of-mass intermolecular total pair correlation function. The theory is found to agree well with the structure predicted by molecular dynamics simulations of the liquid described at the united atom level as well as by molecular dynamics simulations of the liquid of interacting colloidal particles. The authors perform simulations of the liquid of interacting colloidal particles having as input the potential obtained from their analytical total pair correlation function by enforcing the hypernetted-chain closure approximation. Tests systems are polyethylene melts of chains with increasing degrees of polymerization and polymer melts of chains with different chemical architectures. They also discuss the effect of adopting different conventional approximations for intra- and intermolecular monomer structure factors on the accuracy of the coarse-graining procedure, as well as the relevance of higher-order corrections to their expression. [ABSTRACT FROM AUTHOR]

We present a theoretical approach which maps polymer blends onto mixtures of soft-colloidal particles. The analytical mesoscale pair correlation functions reproduce well data from united atom molecular dynamics simulations of polyolefin mixtures without fitting parameters. The theory exactly recovers the analytical expressions for density and concentration fluctuation structure factors of soft-colloidal mixtures (liquid alloys). © 2005 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A mesoscale model of DNA is presented (3SPN.1), extending the scheme previously developed by our group. Each nucleotide is mapped onto three interaction sites. Solvent is accounted for implicitly through a medium-effective dielectric constant and electrostatic interactions are treated at the level of Debye-Hückel theory. The force field includes a weak, solvent-induced attraction, which helps mediate the renaturation of DNA. Model parameterization is accomplished through replica exchange molecular dynamics simulations of short oligonucleotide sequences over a range of composition and chain length. The model describes the melting temperature of DNA as a function of composition as well as ionic strength, and is consistent with heat capacity profiles from experiments. The dependence of persistence length on ionic strength is also captured by the force field. The proposed model is used to examine the renaturation of DNA. It is found that a typical renaturation event occurs through a nucleation step, whereby an interplay between repulsive electrostatic interactions and colloidal-like attractions allows the system to undergo a series of rearrangements before complete molecular reassociation occurs.