  We employ ab initio molecular dynamics to simulate the response of
hydrogenated amorphous silicon to light exposure (Staebler-Wronski effect). We
obtain improved microscopic understanding of PV operation, compute the motion
of H atoms, and modes of light-induced degradation of photovoltaics. We clarify
existing models of light-induced change in aSi:H and show that the Hydrogen
collision model of Branz3 is correct in essentials.
