  Even in a topologically perfect crystal, a moving twin wall will experience
forces due to the discrete nature of the lattice. The potential energy
landscape can be described in terms of one of two parameters: the Peierls
energy, which is the activation energy for domain wall motion in a perfect
crystal; and the Peierls stress, the maximum pinning stress that the potential
can exert. We investigate these parameters in a one order parameter discrete
Landau-Ginzburg model and a classical potential model of the ferroelastic
perovskite CaTiO3. Using the one order parameter model we show that the Peierls
energy scales with the barrier height of the Landau double well potential and
calculate its dependence on the width of the wall numerically. In CaTiO3 we
calculate the Peierls energy and stress indirectly from the one order parameter
model and directly from the interatomic force field. Despite the simplicity of
the one order parameter model, its predictions of the activation energy are in
good agreement with calculated values.
