The Common Concept of Anticooperativity Among Molecules Is Fundamentally Flawed, Based on Novel and Unified Molecular-Wide and Electron Density (MOWeD) Concept of Chemical Bonding

A non-linear (non-additive) increase in stability of hexamers follows an increase in the total number of (i) <b>aad</b> (a double proton acceptor) plus <b>add</b> (a double proton donor) waters commonly linked with anticooperativity and (ii) the total number of intermolecularly delocalized electrons (^intermol<i>N</i>^deloc) in the 3D space occupied by a hexamer. Subsequently, we obtained nearly a perfect linear correlation between increase in the cluster stability and ^intermol<i>N</i>^deloc. Individual water molecules that act as either <b>aad</b> or <b>add</b> (i) delocalize the largest number of electrons throughout a cluster; (ii) are involved in the strongest attractive, hence energy-stabilizing intermolecular interaction with the remaining five waters; (iii) have the most significant quantum component of the intermolecular interaction energy and (iv) relative to six non-interacting water molecules, stabilize a hexamer the most, as quantified by a purposely derived <i>mol</i>-FAMSEC energy term. Clearly, the <b>all-body</b> approach used in the unified, molecular-wide and electron density (MOWeD)-based concept of chemical bonding contradicts the commonly accepted view that <b>aad</b> and <b>add</b> water molecules are involved in anticooperativity in 3D water hexamers. Consequently, we propose here a general definition of cooperativity that should be applicable to any <i>n</i>-membered molecular cluster, namely <i>the quantifiable, classical physics- and quantum-based cooperativity phenomenon is synonymous with the intermolecular <b>all-body</b> delocalization of electrons, leading to the increase in stability of individual molecules on an n-membered cluster formation.</i>