Florian Müller-Plathe

Computer simulation of a polymer electrolyte: Lithium iodide in amorphous poly(ethylene oxide)

Systems of lithium iodide dissolved in poly(ethylene oxide), which are prototypes of polymer electrolytes used, for example, in batteries were studied by means of molecular dynamics simulations. Investigations were aimed at the molecular driving force behind the salt uptake, the mechanism of ion transport, participation of the polymer in ion transport, ion clustering, change of polymer properties by the presence of ions, and ionic conductivity. Particular attention has been given to the differences in behavior between (previously studied) neutral and ionic species dissolved in polymers.

YASP: A molecular simulation package

Abstract Details of the implementation, user interface and file formats of the YASP molecular dynamics program (version 3.0) are described. Version 3.0 has been extensively rewritten with respect to earlier versions. The features now include Coulombic interactions, reaction field approximation, external forces, position restraining, fully vectorised treatment of bond constraints, constraint contributions to the pressure, efficient and well-vectorised evaluation of bonded and nonbonded interactions.

Force field parametrization by weak coupling. Re-engineering SPC water

Abstract A recently developed scheme for the automatic adjustment of force field parameters to experimentally observed properties is applied to the simple-point-charge (SPC) water model. The refinement procedure is based on a first-order coupling of a force-field parameter (say, an atomic charge) to the deviation of a calculated bulk liquid property (e.g. the heat of vaporization) from its ideal value. I.e. the method is very similar in spirit to the weak-coupling scheme used to implement constant-temperature or constant-pressure molecular dynamics. With the method we have refined the charges and the Lennard-Jones diameter of the SPC water model at several state points of high temperature and high pressure. We also have studied how these force-field parameters have to be reoptimized as the cutoff distance is varied.

A molecular dynamics simulation study with a combined quantum mechanical and molecular mechanical potential energy function: Solvation effects on the conformational equilibrium of dimethoxyethane

Solvent effects on the conformational equilibria of dimethoxyethane (DME, CH3–O–CH2–CH2–O–CH3) have been studied using molecular dynamics simulation with a combined molecular mechanical and semiempirical quantum mechanical potential energy function. The potential of mean force around the central O–C–C–O dihedral angle of DME in water was determined using umbrella sampling, with the DME molecule treated by the modified intermediate neglect of diatomic differential overlap (MNDO) method and water molecules described using the extended simple point charge model. This potential of mean force shows the same bias as the gas phase potential energy surface calculated by MNDO: the heights of the barriers are underestimated and the stability of the gauche conformation with respect to the trans conformation is overestimated. However, the calculated stabilization of the gauche state by solvation is in good agreement with experimental results, suggesting a quite reasonable description of this system by the combined po...

Solvent dynamics in swollen polymers

Abstract We report molecular dynamics simulations of benzene-polystyrene systems (0–84.2 wt.%). The composition dependence of calculated solvent diffusion coefficients shows good agreement with experiment and it also follows well the predictions by lattice models. The mobility of solvent molecules in the first solvation shell of the polymer is the same as that in the bulk. The reorientation of benzene molecules in the gel is non-exponential and anisotropic, the reorientation of the ring normal being slower than the in-plane reorientation. This anisotropy increases from 10 0 for neat benzene to 10 3 at the highest polymer concentration.

An All-Atom Force Field for Liquid Ethanol–Properties of Ethanol–Water Mixtures

Abstract An all-atom model of ethanol is presented. It describes a number of properties of liquid ethanol in good agreement with experiment. It has also been tested in conjunction with the simple-point-charge (SPC) water model. The calculated bulk properties of ethanol-water mixtures show reasonable agreement with experimental data where available.

Molecular dynamics study of the mixing and demixing of a binary Lennard-Jones fluid

Dynamic properties of a binary Lennard-Jones mixture at various temperatures and two densities are studied using a molecular dynamics computer simulation starting from mixed and separated initial configurations. After deriving an analytical correction term for finite size effects, the rate of separation is determined as a function of temperature, which is influenced by two counteracting trends: at higher particle velocities demixing becomes faster, but with increasing temperature the separated state becomes less stable. At both densities studied, we observe an increase in the rate of separation with increasing temperature. In a second step, a small number of a third type of particle representing a crude model of an amphiphilic molecule is added and the results are compared with those of the binary mixture case. Owing to a dip in the density at the binary fluid interface, the amphiphilic molecules collect in a slit and as a result, no effect on the separation behaviour of the system is observed. At those t...

PARALLACS: a benchmark for parallel molecular dynamics

Abstract A small molecular dynamics program which, nonetheless, contains all the features typical for present-day general-purpose production codes, is presented. We describe its implementation both at the sequential and the parallel level. A set of four standard benchmarks, deemed typical for the application of molecular dynamics to realistic systems, has been devised and is discussed. The benchmarks have been run on a variety of sequential and parallel architectures and a number of results are reported here. The code, both a sequential version and a PVM-based message-passing parallel version, and the set of benchmarks are publicly available.