Effects of fluctuating hydrodynamic interaction

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Abstract
Dynamical simulations of Gaussian chains with fluctuating hydrodynamic interaction (HI) have been performed for the purpose of evaluating the diffusion constant and intrinsic viscosity from time correlation functions. Equilibrium simulations have also been performed to provide upper and lower bounds for the same quantities. The largest chain used for dynamical work had 56 beads. The effect of fluctuating HI on the diffusion constant is estimated to amount to a 5% decrease in the long chain limit. This decrease seems to be independent of the friction constant assigned to the beads, within statistical and extrapolation errors. However, most of the decrease seems to arise, unexpectedly, in modification of the short time correlation function. Our results for the intrinsic viscosity do not allow extrapolation to a long chain limit that is independent of assigned friction constant. For the smallest friction constant used, corresponding to a Stokes diameter of 0.1 in units of the root-mean-square bond length, the extrapolated decrease in intrinsic viscosity due to fluctuating HI amounts to about 10%. For our largest Stokes diameter of unity, the extrapolated decrease is about 30%. It seems possible that the transport coefficients of long chains are determined by gross configurational properties only if the friction constant is small.