From each starting structure, a 2 ps long trajectory was propagated with a time step of 42 a.u. (1.016 fs) using the NVT ensemble at T = 300 K (the thermostat was applied every 100 fs). The first picosecond of each trajectory was treated as equilibration and the second ps was treated as a production run. Hence, the total simulation time in AIMD was 40 ps; these trajectories were used to collect snapshots for the QM/MM simulations of the ionization spectrum and to compute structural parameters of bulk water. We note that this time is shorter than in the MD simulations, however, the convergence of the radial distribution function, g OO (r), shows that this simulation time is sufficient (e.g., g OO (r) computed from the full MD trajectory of 3 ns and from a 40 ps segment look the same).