Since the KS propagator is non-linear, each propagation step
should be performed self-consistently. In practice, for most
purposes this is not necessary, except perhaps in the first
iterations. This variable holds the number of propagation steps
for which the propagation is done self-consistently.
The special value all_steps forces self-consistency to
be imposed on all propagation steps. A value of 0 means that
self-consistency will not be imposed. The default is 0.
Self-consistency is imposed for all propagation steps.