  We use accurate first principles methods to study the network dynamics of
hydrogenated amorphous silicon, including the motion of hydrogen. In addition
to studies of atomic dynamics in the electronic ground state, we also adopt a
simple procedure to track the H dynamics in light-excited states. Consistent
with recent experiments and computer simulations, we find that dihydride
structures are formed for dynamics in the light-excited states, and we give
explicit examples of pathways to these states. Our simulations appear to be
consistent with aspects of the Staebler-Wronski effect, such as the
light-induced creation of well separated dangling bonds.
