The finite size effects of closed simulations manifest in a free energy minimum for the stable thermodynamic phase resulting from nucleation. This is different to the macroscopic case due to a bounded partition function and a depletion of crystal building blocks that transfer from the parent phase to the nucleating phase. B) Crystal nucleation pathways from solution to crystal represented on a two-dimensional reaction coordinate characterising cluster density and order. The diagonal marks the case for the concomitant increase in solute cluster order with density, indicative of the capillary approximation adopted in CNT. Pathways that deviate from this limiting case include two-step nucleation, where, for example, crystalline order is established in the core of liquid-like precursors, as shown on the right of B. In the case of NaCl nucleation (discussed below), simulations demonstrate a transition from one-step to two-step crystal nucleation that occurs when the supersaturation ratio, 𝑆 = exp(Δ𝜇 𝓁→𝑥𝑡𝑎𝑙 ∕𝑘 B 𝑇 ), is increased far into the metastable zone for phase separation.