 They did this for a simple but approximate model of water called TIP4P/2005.At a supercooling of 19.5 °C, i.e., 19.5 °C below the freezing point of water in their model, they estimate a free energy barrier to nucleation of ice of formula_35.They also estimate a rate of addition of water molecules to an ice nucleus near the top of the barrier of formula_36 and a Zeldovich factor formula_37.