Garbuio, V (Reprint Author), Univ Roma Tor Vergata, ETSF, Via Ric Sci 1, I-00133 Rome, Italy. Univ Roma Tor Vergata, ETSF, I-00133 Rome, Italy. Univ Roma Tor Vergata, CNR, INFM, Dept Phys, I-00133 Rome, Italy. Ecole Polytech Fed Lausanne, Lab Computat Chem & Biochem, CH-1015 Lausanne, Switzerland. Ecole Polytech, Solides Irradies Lab, F-91128 Palaiseau, France.

We present ab initio calculations of the excited state properties of liquid water in the framework of many-body Green's function formalism. Snapshots taken from molecular dynamics simulations are used as input geometries to calculate electronic and optical spectra, and the results are averaged over the different configurations. The optical absorption spectra with the inclusion of excitonic effects are calculated by solving the Bethe-Salpeter equation. The insensitivity of screening effects to a particular configuration make these calculations feasible. The resulting spectra, which are strongly modified by many-body effects, are in good agreement with experiments.