Credit:
Molecular dynamics simulation of nucleation in undercooled copper, revealing a nucleation pathway that traverses a metastable intermediate phase (body-centered cubic, blue) with subsequent transformation to the lowest free energy phase (face-centered cubic, green) initiated at the interface of the metastable phase and the surrounding liquid (liquid particles were removed from the image, for clarity); further phase competition occurs between the face-centered cubic and hexagonal close-packed structures (red) in the vicinity of the interface.