Metashooting: a novel tool for free energy reconstruction from polymorphic phase transition mechanisms.

We introduce a novel scheme for the mechanistic investigation of solid-solid phase transitions, which we dub 'metashooting'. Combining transition path sampling, molecular dynamics and metadynamics, this scheme allows for both a complete mechanistic analysis and detailed mapping of the free energy surface. This is illustrated by performing metashooting calculations on the pressure-induced B4/B3 → B1 phase transition in ZnO. The resulting free energy map helps to clarify the role of intermediate configurations along this activated process and the competition between different mechanistic regimes with superior accuracy. We argue that metashooting can be efficiently applied to a broader class of activated processes.