We combine ab-initio methods and classical molecular dynamics with surface hopping (Tully's least switches approach) to study the time-resolved behavior of molecules in excited states, involving non-adiabatic transitions. The ab-initio potential energy surfaces are not precomputed, but energy, analytic gradient, and non-adiabatic couplings are computed "on the fly" along the trajectories. This allows to study molecules with more degrees of freedom. Since the calculation of non-adiabatic couplings is computationally demanding, we test also approximate approaches to handle these terms. We have applied these techniques to non-stoichiometric alkali-halide clusters, for example Na3F.
Example of results: Simulated femtosecond spectrum of Na3F cluster (red) in comparison with the experimental pump-probe spectrum.