The post-perovskite phase of (Mg,Fe)SiO3 is believed to be the
main mineral phase of the Earth’s lowermost mantle (the D 00
layer). Its properties explain1–6 numerous geophysical obser-
vations associated with this layer — for example, the D 00 discon-
tinuity7, its topography8 and seismic anisotropy within the layer9.
Here we use a novel simulation technique, first-principles
metadynamics, to identify a family of low-energy polytypic
stacking-fault structures intermediate between the perovskite
and post-perovskite phases. Metadynamics trajectories identify
plane sliding involving the formation of stacking faults as the most
favourable pathway for the phase transition, and as a likely
mechanism for plastic deformation of perovskite and post-
perovskite. In particular, the predicted slip planes are {010} for
perovskite (consistent with experiment10,11) and {110} for post-
perovskite (in contrast to the previously expected {010} slip
planes1–4). Dominant slip planes define the lattice preferred
orientation and elastic anisotropy of the texture. The {110} slip
planes in post-perovskite require a much smaller degree of lattice
preferred orientation to explain geophysical observations of
shear-wave anisotropy in the D 00 layer.
