Nuclear Quantum Effects in Neutral Water Clusters at Finite Temperature: Structural Evolution from Two to Three Dimensions

Understanding the structure of bulk water presents a significant challenge due to its intricate hydrogen bond network and dynamic properties. Neutral water clusters, serving as fundamental building blocks, provide key insights into hydrogen bond configurations and intermolecular interactions, thereby establishing a critical foundation for elucidating the behavior of liquid water. In this study, state-of-the-art quantum simulations utilizing a many-body potential for water are employed to investigate the influence of nuclear quantum effects (NQEs) on the structural evolution of neutral water clusters (H₂O)_<i>n</i> (<i>n</i> = 2-10). For the pentamer at finite temperature, quantum simulations demonstrate that NQEs substantially facilitate the transition from two-dimensional (2D) to three-dimensional (3D) configurations. The population of 3D isomers is governed by a synergistic interplay among the effects of thermal fluctuates and NQEs. For water hexamers with fully 3D structures, the quantum simulations uncover a lower-energy pathway for structural evolution from a prism to a book structure via a cage-like intermediate-a pathway not observed in classical simulations. These findings highlight the crucial role of NQEs in the structural evolution of water clusters and provide a theoretical framework to explore the structure and dynamic properties of condensed-phase water.