**Molecular dynamics simulation of fractal aggregate diffusion**

G Pranami and MH Lamm and RD Vigil, PHYSICAL REVIEW E, 82, 051402 (2010).

DOI: 10.1103/PhysRevE.82.051402

The diffusion of fractal aggregates constructed with the method by Thouy
and Jullien **J. Phys. A 27, 2953 (1994)** comprised of N(p) spherical
primary particles was studied as a function of the aggregate mass and
fractal dimension using molecular dynamics simulations. It is shown that
finite-size effects have a strong impact on the apparent value of the
diffusion coefficient (D), but these can be corrected by carrying out
simulations using different simulation box sizes. Specifically, the
diffusion coefficient is inversely proportional to the length of a cubic
simulation box, and the constant of proportionality appears to be
independent of the aggregate mass and fractal dimension. Using this
result, it is possible to compute infinite dilution diffusion
coefficients (D(o)) for aggregates of arbitrary size and fractal
dimension, and it was found that D(o)proportional to N(p)(-1/df), as is
often assumed by investigators simulating Brownian aggregation of
fractal aggregates. The ratio of hydrodynamic radius to radius of
gyration is computed and shown to be independent of mass for aggregates
of fixed fractal dimension, thus enabling an estimate of the diffusion
coefficient for a fractal aggregate based on its radius of gyration.

Return to Publications page