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 ͑MD͒ 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 Ϫ1 (L denoting the linear dimension of the box͒, the decay rate of the Rouse modes is only subject to an L Ϫ3 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 compared quantitatively, showing that the new method allows for much larger time steps. Comparison of the results for both methods indicates systematic deviations due to nonperfect match of the static chain conformations.

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 Kirkwood theory of the diffusion constant, as well as the Akcasu et al. theory of the initial decay rate in dynamic light scattering are generalized for the finite box case, replacing the Oseen tensor by the corresponding Ewald sum. In leading order, the finite-size corrections are inversely proportional to the linear box dimensions. With this modification of the theory taken into account, the Kirkwood formula for the diffusion constant is verified. Moreover, the monomer motions exhibit a scaling that is much closer to Zimm than to Rouse exponents (t2/3 law in the mean square displacement; decay rate of the dynamic structure factor ∝k3). However, the prefactors are not consistent with the theory, indicating that (on the involved short length scales) the dynamics is more complex than the simple hydrodynamic description suggests.

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.

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 crystallisation tendency. In this first manuscript we analyse the structural properties as a function of temperature and the long time or α-relaxation behaviour as observed in the dynamic structure factor and the self-diffusion of the polymer chains. The α-relaxation can be consistently analysed in terms of the mode coupling theory (MCT) of the glass transition. The mode coupling critical temperature, T c , and the exponent, γ, defining the power law divergence of the α-relaxation timescale both depend on the thermodynamic ensemble employed in the simulation.

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