Waters ability to form hydrogen bonds is at the core of many of its astounding properties. Cooperation, or cooperativity, describes the notion that that a molecule forms additional hydrogen bonds more readily, when it is already hydrogen bonded. However, to this day the intricacies of cooperation in real water have not been elucidated. In this work, we set out to improve the current understanding of hydrogen bond cooperationby using a proper basis for its description, namely, its energy. To this end, we use data of the energy decomposition analysis of a molecular dynamics simulation of bulk water and the water surface, which has been been tuned to represent physical properties of real water at ambient temperature as accurately as possible. The energy decomposition analysis, ALMO EDA, offers a way to uniquely determine the energies of hydrogen bonds. We find and quantify a direct dependence of the energy of a hydrogen bond on the energy of other bonds. We further elucidate how cooperation and bond energy alters features of two surface specific spectroscopic methods, namely sum-frequency generation and x-ray absorption. |