Figure 3.

Different water models serve different purposes. (left) Coarse-grained and reduced-dimensionality models. These allow for the most extensive sampling of configurations, and are useful for modeling the statistical mechanics, partition functions, entropies, and heat capacities. (middle) Atomically detailed semiempirical models are used in molecular dynamics and Monte Carlo simulations of liquid and solid states. (middle left) Fixed-charge models. (middle right) Polarizable models. (right) Quantum mechanical (QM) models represent the atomic nuclei and electrons explicitly, for studying bonding. QM modeling is computationally expensive.