  Electron-hole pair creation by an adsorbate incident on a metal surface is
described using \textit{ab initio} methods. The approach starts with standard
first principles electronic structure theory, and proceeds to combine
classical, quantum oscillator and time dependent density functional methods to
provide a consistent description of the non-adiabatic energy transfer from
adsorbate to substrate. Of particular interest is the conservation of the total
energy at each level of approximation, and the importance of a spin transition
as a function of the adsorbate/surface separation. Results are presented and
discussed for H and D atoms incident on the Cu(111) surface.
