Complete titanium HCP to omega transformation mechanism

Under pressure, titanium transforms from a hexagonal-closed-packed (hcp) structure to a high pressure omega phase. The phase transition from hcp to omega is known to be martensitic, but the transformation mechanics have not been described quantitatively. To find the most probable mechanism, we produced a set of possible mechanisms by enumerating common subgroups of the two structures. The list was reduced by keeping only mechanisms with the smallest strains. An estimated energy barrier for each remaining mechanism was calculated using a tight-binding model for titanium. From this set of approximate barriers, the mechanisms with the smallest barriers were chosen, and the true energy barrier was calculated using an ab initio method. This barrier was calculated as a function of pressure, allowing us to finally predict the mechanics of the transformation, as well as the zero temperature transformation pressure.