1202.4796 (Pratyush Tiwary et al.)

Realistic time-scale fully atomistic simulations of surface nucleation
of dislocations in pristine nanopillars    [PDF]

Pratyush Tiwary, Axel van de Walle

We use our recently proposed accelerated dynamics algorithm (Tiwary and van
de Walle, 2011) to calculate temperature and stress dependence of activation
free energy for surface nucleation of dislocations in pristine Gold nanopillars
under realistic loads. While maintaining fully atomistic resolution, we achieve
the fraction of a second time-scale regime. We find that the activation free
energy depends significantly and non-linearly on the driving force (stress or
strain) and temperature, leading to very high activation entropies. We also
perform compression tests on Gold nanopillars for strain-rates varying between
7 orders of magnitudes, reaching as low as 10^3/s. Our calculations bring out
the perils of high strain-rate Molecular Dynamics calculations: we find that
while the failure mechanism for <001> compression of Gold nanopillars remains
the same across the entire strain-rate range, the elastic limit (defined as
stress for nucleation of the first dislocation) depends significantly on the
strain-rate. We also propose a new methodology that overcomes some of the
limits in our original accelerated dynamics scheme (and accelerated dynamics
methods in general). We lay out our methods in sufficient details so as to be
used for understanding and predicting deformation mechanism under realistic
driving forces for various problems.

View original: http://arxiv.org/abs/1202.4796