Investigating prenucleation species is particularly useful to identify systems that may undergo phase separation following the PNC pathway and other nonclassical crystallisation routes. In particular, many studies have considered the structure and stability of CaCO 3 assemblies that emerge in solution and the effects of additives and solution environment on their properties. These studies have demonstrated that entropy drives the formation of PNCs and questioned the relationship between PNCs and microscopic precursors to dense liquids . Generally, it was observed that organic additives stabilise liquid-like assemblies that form prior to crystallisation. Predicting the phase behaviour in systems that follow PNC separation requires evaluation of the equilibrium constant for monomer association, as discussed in section 2. Enhanced sampling simulations, particularly Umbrella Sampling and metadynamics, have been successfully applied to evaluate these constants, which corroborate experimental measurements. Both biased and unbiased MD simulations were informative in predicting the structure and dynamic properties of the PNCs and determining the thermodynamic driving forces for their formation. In this regard, the application of simulations has been critical to understanding and evolving theories for the PNC pathway.