Ab-initio calculations of Many-Body effects in liquids: the electronic excitations of water

We present ab-initio calculations of the excited state properties of liquid water in the framework of Many-Body Greens 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. These calculations are made possible by exploiting the insensitivity of screening effects to a particular configuration. The resulting spectra are strongly modified by many-body effects, both concerning peak energies and lineshapes, and are in good agreement with experiments.