Comparison of computational water models for simulation of calcium–silicate–hydrate

Calcium silicate hydrate, or C–S–H, is the chief hydration product of Portland cement. The structure of the C–S–H phase within cement has been proposed and developed via molecular simulations. In such simulations, empirical interatomic potentials for water molecules within C–S–H are adopted to govern the position and relative motion of this key constituent. Initial simulations and force fields of C–S–H have assumed the simplest molecular model of H2O termed “single point charge” or SPC, but this choice has not been validated by comparison with other computational models of water that confer additional bond flexibility or charge distribution. To enable efficiently computational modeling of C–S–H and to explore the role that H2O plays in maintaining C–S–H structure and properties, the choice of an efficient and accurate water model is critical. Here, we consider five distinct, classical atomistic water models (SPC, TIP3P, TIP4P, TIP4P05, and TIP5P) to determine the effects of these computational simplifications on C–S–H properties. Quantitative comparison of all five water models shows that the appropriate water model depends on the C–S–H characteristics of interest. Among these models, both SPC and TIP5P models successfully predict key properties of the structure and elastic constants of C–S–H, as well as the dynamics of water molecules within C–S–H.