  In this paper we discuss the application of current it ab initio computer
simulation techniques to hydrogenated amorphous silicon (a-Si:H). We begin by
discussing thermal fluctuation in the number of coordination defects in the
material, and its temperature dependence. We connect this to the ``fluctuating
bond center detachment" mechanism for liberating H bonded to Si atoms. Next,
from extended thermal MD simulation, we illustrate various mechanisms of H
motion. The dynamics of the lattice is then linked to the electrons, and we
point out that the squared electron-lattice coupling (and the thermally-induced
mean square variation in electron energy eigenvalues) is robustly proportional
to the localization of the conjugate state, if localization is measured with
inverse participation ratio. Finally we discuss the Staebler-Wronski effect
using these methods, and argue that a sophisticated local heating picture
(based upon reasonable calculations of the electron-lattice coupling and
molecular dynamic simulation) explains significant aspects of the phenomenon.
