One of the two goals of this study is to understand the effect of the simulation protocol on the computed spectra. We begin with comparing the results of the MD and AIMD simulations. Fig. (top panel) compares the spectra constructed using the MD and AIMD snapshots. In this calculation, we used the smallest QM size (5 waters only, the rest being treated by point charges) and constructed the spectra using the IE of the central water molecule. The two simulations yield essentially identical spectra, both in terms of the band FIG. : Theoretical 1s O spectra of liquid water computed using the minimal QM system (5 waters) and assembled using the IE of the central water molecule. Top: Spectra constructed from the MD (TIP3P) and AIMD trajectories (400 snapshots). Bottom: Spectra constructed from the MD trajectory using different number of snapshots. All spectra were obtained using gaussians with FWHM = 0.2 eV, except for the black trace in the right panel which was produced using 0.05 eV FWHM to show the intrinsic roughness of the spectrum produced from the 3,000 snapshots.