Transition state analysis of solid-solid transformations in nanocrystals

A systematic simulation methodology is introduced for the accurate determination of experimentally measurable quantities characterizing solid-solid phase transformations under pressure. The atomistic mechanisms of nucleation and growth in a structural transformation of pressurized CdSe nanocrystals are identified using transition path sampling computer simulation. A committor-based transition state analysis is applied to extract activation enthalpies and activation volumes from transformation pathways at experimental conditions. The qualitative dependence of activation enthalpies on nanocrystal size is in good agreement with experimental data and supports the observed nucleation mechanism, which is characterized by a critical nucleus of elongated shape located on the crystal surface. Based on committor distributions along typical transformation pathways, the coordination number is identified as a suitable reaction coordinate for the process. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3253700]