  To predict the radiative forcing of clouds it is necessary to know the rate
with which ice homogeneously nucleates in supercooled water. Such rate is often
measured in drops to avoid the presence of impurities. At large supercooling
small (nanoscopic) drops must be used to prevent simultaneous nucleation
events. The pressure inside such drops is larger than the atmospheric one by
virtue of the Laplace equation. In this work, we take into account such
pressure raise in order to predict the nucleation rate in droplets using the
TIP4P/Ice water model. We start from a recent estimate of the maximum drop size
that can be used at each supercooling avoiding simultaneous nucleation events
[Espinosa et al. J. Chem. Phys., 2016]. We then evaluate the pressure inside
the drops with the Laplace equation. Finally, we obtain the rate as a function
of the supercooling by interpolating our previous results for 1 and 2000 bar
[Espinosa et al. Phys. Rev. Lett. 2016] using the Classical Nucleation Theory
expression for the rate. This requires, in turn, interpolating the ice-water
interfacial free energy and chemical potential difference. The TIP4P/Ice rate
curve thus obtained is in good agreement with most droplet-based experiments.
In particular, we find a good agreement with measurements performed using
nanoscopic drops, that are currently under debate. The successful comparison
between model and experiments suggests that TIP4P/Ice is a reliable model to
study the water-to-ice transition and that Classical Nucleation Theory is a
good framework to understand it.
