Microscopic dynamics and excited state properties of liquid water

Water is the major chemical constituent of our planet's surface and it is essential for living organism survival; many biochemical and industrial processes occur in aqueous solution and the role of the solvent in the reactions is crucial. The comprehension of the chemical and physical nature of water has been a long-standing goal of science, and liquid water continues to attract intense interest and motivate a large number of experimental and theoretical works. Recently, however, the theoretical studies of water have mostly focused on its structure and ground state properties whereas less effort has been dedicated to its electronic structure and optical absorption spectrum. As a consequence, experimental data about excited states are not yet completely understood. Simultaneously, in the last years, great attention has been devoted to the study of water confined in different nanoporous systems, or in proximity of macromolecules and surfaces, because of its biological and technological importance (water in biology is always confined). Up to now, however, there is no general theory predicting the behavior of confined liquids or the relative importance of surface interaction versus confinement. The present work focuses on two complementary aspects of water: its excited state properties, very important in many chemical reactions and therefore fundamental to advance in many research fields, and the proton microscopic dynamics in confined water, which is interesting for many biological processes such as catalysis, protein folding or ionic transport in membranes. These topics are faced with different investigative approaches, both theoretical and experimental. The electronic and optical properties of liquid water are studied with ab-initio theoretical calculations, taking into account both self-energy and excitonic effects in the framework of many-body perturbation theory. The study of the proton microscopic dynamics of confined water has been instead made with deep inelastic neutron scattering experiments, performed at the ISIS spallation neutron source.