Numerical calculation of the melting phase diagram of low molecular-weight polyethylene

Das, Chinmay; Frenkel, Daan

doi:10.1063/1.1568934

Cited by 6 publications

(3 citation statements)

References 43 publications

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“…We used three different all-atom force fields in our simulations: the OPLS-AA force field, 20 the force field of Borodin and Smith, 21,22 which has been applied to alkanes and perfluoroalkanes, 23,24 and the Flexible Williams force field of Tobias et al, 25 which has previously been applied to alkanes and other organic molecules. [26][27][28] We chose all-atom models rather than more computationally efficient united atom models because united atom models do not give the correct packing for low temperature alkane crystals. 11 All three force fields explicitly include harmonic bond stretch, harmonic angle, and dihedral intramolecular potentials.…”

Section: A Simulation Detailsmentioning

confidence: 99%

Crystal and rotator phases of n-alkanes: A molecular dynamics study

Wentzel

Milner

2010

The Journal of Chemical Physics

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Normal alkanes have a simple molecular structure, but display a surprising variety of ordered phases, including an orthorhombic crystal, followed on heating by two partially ordered rotator phases RI and RII. These phases are interesting both because of the weakly first-order transitions that separate them, and because rotator phases are implicated in the nucleation of crystals in polyethylene. To understand this interesting and technologically important phenomenon, a clear picture of the rotator phase is essential. We conducted all-atom simulations of pure C(23) and mixed C(21)-C(23) normal alkanes. Among potentials we tried, only Flexible Williams gave good agreement with the experimental sequence of phases and transition temperatures. Physical properties of the simulated phases, including lattice dimensions and transition entropy between orthorhombic and rotator RII phase are in good agreement with experiment. We define order parameters for investigating pretransitional fluctuations in RI and RII phases; we observed only very short-range correlations in these phases, but slower temperature scans may be necessary to properly investigate these weakly first-order transitions.

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Section: A Simulation Detailsmentioning

confidence: 99%

Crystal and rotator phases of n-alkanes: A molecular dynamics study

Wentzel

Milner

2010

The Journal of Chemical Physics

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“…Such interaction potentials obtained for small molecules can also be used in atomistic simulations of oligomers and moderately long chains. In all-atom (AA) approaches, ,, for example, one explicitly describes all atoms in the simulation, e.g., the carbon atoms with the chemically bonded hydrogen atoms. However, this approach becomes inefficient for macromolecules, although it can be successfully applied to small and moderately large molecules.…”

Section: Introductionmentioning

confidence: 99%

How Well Can Coarse-Grained Models of Real Polymers Describe Their Structure? The Case of Polybutadiene

Yelash

Müller

Paul

et al. 2006

J. Chem. Theory Comput.

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Coarse-graining of chemical structure of macromolecules in the melt is investigated using extensive molecular dynamics simulation data which are based on a united atom force-field model of polybutadiene. Systematically increasing the number, n, of the united atoms approximated by an effective coarse-grained monomer, we study the influence of degree of coarse-graining on the structure functions such as the segment-segment intermolecular and intramolecular correlation functions. These results are compared to Monte Carlo simulations of the corresponding coarse-grained bead-spring model and Chen-Kreglewski potential for chain molecules. In contrast to the atomistic chemically realistic model of polybutadiene, the bending and torsional potentials are not included into the coarse-grained models. Nevertheless, for a range of intermediate values of n a good qualitative agreement between intra- and intermolecular coarse-grained correlations of the atomistic model and the coarse-grained bead-spring model is found on large and intermediate length scales, but deviations occur on length scales well below one nanometer. The structure functions obtained for the Chen-Kreglewski chains exhibit many artificial features.

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“…Table 3 gives the values of the different parameters for the side chain-side chain and the spin-spin potentials. k length-bond and k angle are fixed to the values used for CC bonds in alkanes [23]. k angle-spin was chosen to give some flexibility to the hydrogen bonds.…”

Section: Modelmentioning

confidence: 99%

Simple off-lattice model to study the folding and aggregation of peptides

Combe

Frenkel

2007

Molecular Physics

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We present a numerical study of a new protein model. This off-lattice model takes into account both the hydrogen bonds and the amino-acid interactions. It reproduces the folding of a small protein (peptide): morphological analysis of the conformations at low temperature shows two well-known substructures -helix and -sheet depending on the chosen sequence. The folding pathway in the scope of this model is studied through a free-energy analysis. We then study the aggregation of proteins. Proteins in the aggregate are mainly bound via hydrogen bonds. Performing a free-energy analysis we show that the addition of a peptide to such an aggregate is not favourable. We qualitatively reproduce the abnormal aggregation of proteins in prion diseases.

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Numerical calculation of the melting phase diagram of low molecular-weight polyethylene

Cited by 6 publications

References 43 publications

Crystal and rotator phases of n-alkanes: A molecular dynamics study

Crystal and rotator phases of n-alkanes: A molecular dynamics study

How Well Can Coarse-Grained Models of Real Polymers Describe Their Structure? The Case of Polybutadiene

Simple off-lattice model to study the folding and aggregation of peptides

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