Predicting the Solvent Properties of Supercritical Water by Integrating Solubility Parameter Theory and Molecular Force Fields

ABSTRACT Supercritical water (SCW) possesses exceptional solvent power, yet accurately predicting its solvent properties remains challenging. Conventional approaches often fail in the supercritical region and lack a solid physical basis. Here, a generalizable “hydrogen‐bond identification first” energy decomposition framework is introduced to directly compute SCW's three‐component solubility parameters from molecular force fields. Analysis along isothermal and isochoric paths reveals that the solvent behavior of SCW results from a competition between direct physical effects, driven by changes in intermolecular proximity and thermal disruption, and indirect network effects arising from the dynamic evolution of the hydrogen‐bond network. The dimensionless ratio | E hb |/RT serves as a physical criterion, with a threshold of 1.0 marking the crossover from hydrogen‐bond‐dominated to thermal‐dominated behavior. Crucially, fluid density primarily determines the absolute magnitude of cohesive interactions, whereas temperature functions as a key variable to selectively redistribute energy among dispersion, polar, and hydrogen‐bonding contributions. Applied to the solvation of heavy nonpolar solutes, the framework identifies an optimal solubility parameter window located in a mild, low‐density regime, favoring efficient miscibility. This work elevates solvent tuning from empirical correlation to mechanistic‐driven prediction, offering a scientific strategy to reconcile process efficiency with sustainable, mild operating conditions.