It was recalled that computer simulations had previously been used to deduce the

atomic-scale properties of the cores of screw dislocations in forsterite by direct

calculation, using parameterized potentials and a Peierls-Nabarro model using

density functional theory. It was shown that, for the [001] screw dislocation, the

parameterized potentials reproduced key features of generalized stacking fault

energies when compared with density functional theory results. However, the

predicted structure of the dislocation core differed for the direct simulations and for

the Peierls-Nabarro model. The [001] screw dislocation was shown to have a lowenergy

non-planar core. It was suggested that, for this dislocation to move its core,

it might need to change its structure and form a high-energy planar structure

similar to that deduced using the Peierls-Nabarro model. This could lead to

dislocation motion via an unlocking-locking mechanism and explain the common

experimental detection of long straight screw dislocation segments in deformed

olivine.

Evidence from Numerical Modelling for 3D Spreading of [001] Screw Dislocations

in Mg2SiO4 Forsterite. P.Carrez, A.M.Walker, A.Metsue, P.Cordier: Philosophical

Magazine, 2008, 88[16], 2477-85