  The semiclassical description of the dynamics of wave packets in periodic
potentials and subject to an applied force relies on the concepts of effective
mass and anomalous transport. This picture is valid if the force changes slowly
in time and space, so that the particle described by the wave packet has time
to respond according to the properties of the lattice. We analyze the dynamical
corrections to this picture when a uniform force is suddenly applied,
identifying separate corrections to the usual group and anomalous velocities.
We find approximate semianalytical expressions for generalized "dynamical"
group and anomalous velocities, and the associated accelerations. We use a
two-dimensional optical lattice with finite Berry curvature to illustrate the
semianalytical approximation in a regime where the dynamical corrections are
significant, suggesting the possibility of experiments to detect them; we
compare the results with a full numerical solution, showing excellent agreement
for weak forces.
