Exploring the mechanism of phase transitions between the hexagonal close-packed and the cuboidal structures

By introducing appropriate lattice parameters for a bi-lattice smoothly connecting the hexagonal close-packed (hcp) with the cuboidal structures, namely the body-centered (bcc) and the face centered cubic (fcc) lattices, we were able to map out the minimum energy path for a Burgers-Bain type of phase transition. We demonstrate that for three different models applied, i.e. the kissing hard-sphere model, the Lennard-Jones potential, and density functional theory for metallic lithium, the direct transition path is always from hcp to fcc with a separate path leading from fcc to bcc. This solves, at least for the models considered here, a long-standing controversy of whether or not fcc acts as an intermediate phase in martensitic type of phase transitions.