  The early planetesimal growth proceeds through a sequence of sticking
collisions of dust agglomerates. Very uncertain is still the relative velocity
regime in which growth rather than destruction can take place. The outcome of a
collision depends on the bulk properties of the porous dust agglomerates.
Continuum models of dust agglomerates require a set of material parameters that
are often difficult to obtain from laboratory experiments. Here, we aim at
determining those parameters from ab-initio molecular dynamics simulations. Our
goal is to improveon the existing model that describe the interaction of
individual monomers. We use a molecular dynamics approach featuring a detailed
micro-physical model of the interaction of spherical grains. The model includes
normal forces, rolling, twisting and sliding between the dust grains. We
present a new treatment of wall-particle interaction that allows us to perform
customized simulations that directly correspond to laboratory experiments. We
find that the existing interaction model by Dominik & Tielens leads to a too
soft compressive strength behavior for uni and omni-directional compression.
Upon making the rolling and sliding coefficients stiffer we find excellent
agreement in both cases. Additionally, we find that the compressive strength
curve depends on the velocity with which the sample is compressed. The modified
interaction strengths between two individual dust grains will lead to a
different behaviour of the whole dust agglomerate. This will influences the
sticking probabilities and hence the growth of planetesimals. The new parameter
set might possibly lead to an enhanced sticking as more energy can be stored in
the system before breakup.
