(476e) Nucleus-Size Pinning for Determination of Nucleation Free-Energy Barriers and Nucleus Geometry

Authors: 
Sharma, A. K., Cornell University
Escobedo, F. A., Cornell University
Classical Nucleation Theory (CNT) has recently been used in conjunction with a seeding approach to simulate nucleation phenomena at small-to-moderate supersaturation conditions when large free-energy barriers ensue. In this study, the conventional seeding approach [J.R. Espinosa, C. Vega, C. Valeriani, and E. Sanz, J. Chem. Phys. 144, 034501 (2016)] is improved by a novel, more robust method to estimate nucleation barriers. Inspired by the interfacial pinning approach [U. R. Pedersen, J. Chem. Phys. 139, 104102 (2013)] used before to determine conditions where two phases coexist, the seed of the incipient phase is pinned to a preselected size to iteratively drive the system toward the conditions where the seed becomes a critical nucleus. We call this technique nucleus-size pinning (NSP). The proposed technique is first validated by estimating the critical nucleation conditions for the disorder-to-order transition in hard spheres, and then applied to simulate and characterize the highly non-trivial (prolate) morphology of the critical crystal nucleus in hard gyrobifastigia. A generalization of CNT is used to account for nucleus asphericity and predict nucleation free-energy barriers for gyrobifastigia. These predictions of nuclei shape and barriers are validated by independent umbrella sampling calculations. With another application of CNT, we are able to determine interfacial tensions for these systems within a single simulation, which match those estimated by standard techniques. Further, we discuss applications of NSP for solid phase nucleation in other systems.