Toward mitigating the impact of non-bulk defects on describing water structure in salt aqueous solutions: Characterizing solution density with a network-based structural indicator.

This article focuses on introducing and validating a network-based structural indicator called the average cluster number (ω̄_c) to characterize intrinsic structural properties of water molecules in both neat water and salt aqueous solutions. Developed to mitigate the impact of non-bulk defects caused by ions occupying neighboring space, ω̄_c is computed from water molecule networks constructed via molecular dynamics simulations using the TIP4P/2005 water model and the Madrid-2019 force field. The study demonstrates that ω̄_c effectively distinguishes intrinsic water structural changes from ion-induced spatial disruptions, capturing temperature- and concentration-dependent variations in solution density and revealing that ions with higher charge density (e.g., Ca²⁺) cause stronger disruption than those with larger ionic radius but lower charge (e.g., K⁺). The findings underscore the importance of addressing non-bulk defects for accurate structural analysis in solutions and suggest that ω̄_c provides a consistent, correction-free approach applicable across different salt solutions, though it may blur local structural details and could benefit from further refinement incorporating molecular orientation or energy considerations.