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Burkhard Dünweg

Bio: Burkhard Dünweg is an academic researcher from Max Planck Society. The author has contributed to research in topics: Monte Carlo method & Lattice Boltzmann methods. The author has an hindex of 34, co-authored 93 publications receiving 4732 citations. Previous affiliations of Burkhard Dünweg include Technische Universität Darmstadt & Monash University.


Papers
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Journal ArticleDOI
TL;DR: In this article, a molecular dynamics simulation of a single polymer chain in a good solvent is presented, where the latter is modeled explicitly as a bath of particles, and a first principle microscopic test of the hydrodynamic Kirkwood-Zimm theory of the chain's Brownian motion is provided.
Abstract: Results of a molecular dynamics simulation of a single polymer chain in a good solvent are presented. The latter is modeled explicitly as a bath of particles. This system provides a first‐principles microscopic test of the hydrodynamic Kirkwood–Zimm theory of the chain’s Brownian motion. A 30 monomer chain is studied in 4066 solvent particles as well as 40/4056 and 60/7940 systems. The density was chosen rather high, in order to come close to the ideal situation of incompressible flow, and to ensure that diffusive momentum transport is much faster than particle motions. In order to cope with the numerical instability of microcanonical algorithms, we generate starting states by a Langevin simulation that includes a coupling to a heat bath, which is switched off for the analysis of the dynamics. The long range of the hydrodynamic interaction induces a large effect of finite box size on the diffusive properties, which is observable for the diffusion constants of both the chain and the solvent particles. The ...

471 citations

Journal ArticleDOI
TL;DR: D dissipative particle dynamics is discussed as a thermostat to molecular dynamics, and some of its virtues are highlighted, including universal applicability irrespective of the interatomic potential.
Abstract: We discuss dissipative particle dynamics as a thermostat to molecular dynamics, and highlight some of its virtues: (i) universal applicability irrespective of the interatomic potential; (ii) correct and unscreened reproduction of hydrodynamic correlations; (iii) stabilization of the numerical integration of the equations of motion; and (iv) the avoidance of a profile bias in boundary-driven nonequilibrium simulations of shear flow. Numerical results on a repulsive Lennard-Jones fluid illustrate our arguments.

406 citations

Journal ArticleDOI
TL;DR: In this paper, a new efficient method for simulating polymer-solvent systems which combines a lattice Boltzmann approach for the fluid with a continuum molecular-dynamics (MD) model for the polymer chain is established.
Abstract: In this paper we establish a new efficient method for simulating polymer–solvent systems which combines a lattice Boltzmann approach for the fluid with a continuum molecular-dynamics (MD) model for the polymer chain. The two parts are coupled by a simple dissipative force while the system is driven by stochastic forces added to both the fluid and the polymer. Extensive tests of the new method for the case of a single polymer chain in a solvent are performed. The dynamic and static scaling properties predicted by analytical theory are validated. In this context, the influence of the finite size of the simulation box is discussed. While usually the finite size corrections scale as L−1 (L denoting the linear dimension of the box), the decay rate of the Rouse modes is only subject to an L−3 finite size effect. Furthermore, the mapping to an existing MD simulation of the same system is done so that all physical input values for the new method can be derived from pure MD simulation. Both methods can thus be com...

363 citations

Book ChapterDOI
TL;DR: In this article, numerical simulations of the dynamics of particles immersed in a continuum solvent have been studied and a general overview of the various simulation methods that have been developed to cope with the resulting computational problems.
Abstract: This article concerns numerical simulations of the dynamics of particles immersed in a continuum solvent. As prototypical systems, we consider colloidal dispersions of spherical particles and solutions of uncharged polymers. After a brief explanation of the concept of hydrodynamic interactions, we give a general overview of the various simulation methods that have been developed to cope with the resulting computational problems. We then focus on the approach we have devel- oped, which couples a system of particles to a lattice-Boltzmann model representing the solvent degrees of freedom. The standard D3Q19 lattice-Boltzmann model is de- rived and explained in depth, followed by a detailed discussion of complementary methods for the coupling of solvent and solute. Colloidal dispersions are best de- scribed in terms of extended particles with appropriate boundary conditions at the surfaces, while particles with internal degrees of freedom are easier to simulate as an arrangement of mass points with frictional coupling to the solvent. In both cases, particular care has been taken to simulate thermal fluctuations in a consistent way. The usefulness of this methodology is illustrated by studies from our own research, where the dynamics of colloidal and polymeric systems has been investigated in both equilibrium and nonequilibrium situations.

325 citations

Journal ArticleDOI
TL;DR: In this article, the authors present molecular-dynamics simulations of the thermal glass transition in a dense model polymer liquid and analyze the structural properties as a function of temperature and the long time or \ensuremath{\alpha}-relaxation behavior as observed in the dynamic structure factor and the self-diffusion of the polymer chains.
Abstract: We present molecular-dynamics simulations of the thermal glass transition in a dense model polymer liquid. We performed a comparative study of both constant volume and constant pressure cooling of the polymer melt. Great emphasis was laid on a careful equilibration of the dense polymer melt at all studied temperatures. Our model introduces competing length scales in the interaction to prevent any crystallization tendency. In this first manuscript we analyze the structural properties as a function of temperature and the long time or \ensuremath{\alpha}-relaxation behavior as observed in the dynamic structure factor and the self-diffusion of the polymer chains. The \ensuremath{\alpha} relaxation can be consistently analyzed in terms of the mode coupling theory of the glass transition. The mode coupling critical temperature ${T}_{c},$ and the exponent \ensuremath{\gamma} defining the power law divergence of the \ensuremath{\alpha}-relaxation time scale, both depend on the thermodynamic ensemble employed in the simulation.

239 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, three parallel algorithms for classical molecular dynamics are presented, which can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors.

32,670 citations

01 May 1993
TL;DR: Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems.
Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

29,323 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present a new molecular dynamics algorithm for sampling the canonical distribution, where the velocities of all the particles are rescaled by a properly chosen random factor.
Abstract: The authors present a new molecular dynamics algorithm for sampling the canonical distribution. In this approach the velocities of all the particles are rescaled by a properly chosen random factor. The algorithm is formally justified and it is shown that, in spite of its stochastic nature, a quantity can still be defined that remains constant during the evolution. In numerical applications this quantity can be used to measure the accuracy of the sampling. The authors illustrate the properties of this new method on Lennard-Jones and TIP4P water models in the solid and liquid phases. Its performance is excellent and largely independent of the thermostat parameter also with regard to the dynamic properties.

11,327 citations

Journal ArticleDOI
TL;DR: A review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena as mentioned in this paper.
Abstract: Microfabricated integrated circuits revolutionized computation by vastly reducing the space, labor, and time required for calculations. Microfluidic systems hold similar promise for the large-scale automation of chemistry and biology, suggesting the possibility of numerous experiments performed rapidly and in parallel, while consuming little reagent. While it is too early to tell whether such a vision will be realized, significant progress has been achieved, and various applications of significant scientific and practical interest have been developed. Here a review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena. Specifically, this review explores the Reynolds number Re, addressing inertial effects; the Peclet number Pe, which concerns convective and diffusive transport; the capillary number Ca expressing the importance of interfacial tension; the Deborah, Weissenberg, and elasticity numbers De, Wi, and El, describing elastic effects due to deformable microstructural elements like polymers; the Grashof and Rayleigh numbers Gr and Ra, describing density-driven flows; and the Knudsen number, describing the importance of noncontinuum molecular effects. Furthermore, the long-range nature of viscous flows and the small device dimensions inherent in microfluidics mean that the influence of boundaries is typically significant. A variety of strategies have been developed to manipulate fluids by exploiting boundary effects; among these are electrokinetic effects, acoustic streaming, and fluid-structure interactions. The goal is to describe the physics behind the rich variety of fluid phenomena occurring on the nanoliter scale using simple scaling arguments, with the hopes of developing an intuitive sense for this occasionally counterintuitive world.

4,044 citations

Journal ArticleDOI
TL;DR: In this article, an extensive molecular-dynamics simulation for a bead spring model of a melt of linear polymers is presented, where the number of monomers N covers the range from N=5 to N=400.
Abstract: We present an extensive molecular‐dynamics simulation for a bead spring model of a melt of linear polymers. The number of monomers N covers the range from N=5 to N=400. Since the entanglement length Ne is found to be approximately 35, our chains cover the crossover from the nonentangled to the entangled regime. The Rouse model provides an excellent description for short chains N

3,232 citations