  We introduce a novel scheme for the mechanistic investigation of solid-solid
phase transitions, which we dub \textit{metashooting}. Combining transition
path sampling molecular dynamics and metadynamics, this scheme allows for both
a complete mechanistic analysis and a detailed mapping of the free energy
surface. This is illustrated by performing \textit{metashooting} calculations
on the pressure-induced B4/B3 $\rightarrow$ 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
\textit{metashooting} can be efficiently applied to a broader class of
activated processes
