Free-energy reconstruction from stable clusters (FRESC): A new method to evaluate nucleation barriers from simulation

Abstract

We present a simulation technique to evaluate the most important quantity for nucleation processes: the nucleation barrier, i.e., the free energy of formation of the critical cluster. The method is based on stabilizing a small cluster by simulating it in the NVT ensemble and using the thermodynamics of small systems to convert the properties of this stable cluster into the Gibbs free energy of formation of the critical cluster. We demonstrate this approach using condensation in a Lennard-Jones truncated and shifted fluid as an example, showing an excellent agreement with previous umbrella sampling simulations. The method is straightforward to implement, computationally inexpensive, requires only a small number of particles comparable to the critical cluster size, does not rely on the use of classical nucleation theory, and does not require any cluster definition or reaction coordinate. All of these advantages hold the promise of opening the door to simulate nucleation processes in complex molecules of atmospheric, chemical, or pharmaceutical interest that cannot be easily simulated with current techniques.