Understanding the structure and hydrogen bonding network of (H2O)32 and (H2O)33: an improved Monte Carlo temperature basin paving (MCTBP) method and quantum theory of atoms in molecules (QTAIM) analysis

Abstract

Large water clusters are of particular interest because of their connection to liquid water and the intricate hydrogen bonding networks they possess. Generally, clusters above (H₂O)₂₅ are cage-like; however, the diversity of their hydrogen bonding can be enormous and is related to the stability of the cluster. Two main challenges for understanding hydrogen bonding networks are how to determine a few low energy minima in the extremely rugged energy surface of large water clusters and how to rationalize the relative stability of different structures of a cluster based on simple chemical concepts, particularly when they are very close in energy. In the current work, an improved version of the Monte Carlo Temperature Basin Paving (MCTBP) method has been used to find low energy structures of (H₂O)₃₂ and (H₂O)₃₃ as an answer to the first challenge. Previously, the MCTBP method has been applied to large water clusters with reasonable success. In this work, we have changed the Monte Carlo acceptance/rejection condition to make the calculation more efficient. After finding several structures at either the same or lower energy of previously known structures, the quantum theory of atoms in molecules (QTAIM) method has been applied to analyze the relationship between the stability and polarized charges on each water molecule in a cluster. Overall, an increase of the polarized charge on the oxygen atom was found to stabilize the energy of a water molecule in a cluster.