We present a numerical model of dislocation cores in Mg2SiO4 forsterite based on the Peierls-Nabarro model and using generalised stacking faults as an input. The generalised stacking faults have been calculated from ab initio density-functional theory using VASP. Core profiles, atomic models and Peierls stresses are proposed for dislocations from the following slip systems: [100](010), [100](001), [100]{021}, [001](010), [001](100) and [001]{110}. Calculations have been performed at 0 and 10 GPa, to investigate the influence of pressure. We show that [100] dislocations have narrow cores when [001] dislocations tend to spread into (100) and {110} planes. A strong softening effect is found with pressure on the [001](010) slip system. Our study emphasizes the influence of lattice friction on plastic deformation of forsterite with, beyond Peierls stresses, possible effects related to non-planar core structures.

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