  We employ Non-equilibrium Green's functions (NEGF) to describe the real-time
dynamics of an adsorbate-surface model system exposed to ultrafast laser
pulses. For a finite number of electronic orbitals, the system is solved
exactly and within different levels of approximation. Specifically i) the full
exact quantum mechanical solution for electron and nuclear degrees of freedom
is used to benchmark ii) the Ehrenfest approximation (EA) for the nuclei, with
the electron dynamics still treated exactly. Then, using the EA, electronic
correlations are treated with NEGF within iii) 2nd Born and with iv) a recently
introduced hybrid scheme, which mixes 2nd Born self-energies with
non-perturbative, local exchange-correlation potentials of Density Functional
Theory (DFT). Finally, the effect of a semi-infinite substrate is considered:
we observe that a macroscopic number of de-excitation channels can hinder
desorption. While very preliminary in character and based on a simple and
rather specific model system, our results clearly illustrate the large
potential of NEGF to investigate atomic desorption, and more generally, the non
equilibrium dynamics of material surfaces subject to ultrafast laser fields.
