FCC-BCC phase transition in iron under a periodic boundary condition

Ey using isobaric-isothermal molecular dynamics (MD) technique and many-bod y effective potential, we investigate the martensitic transformation in iro n. To describe structural phase transitions, we adopt the Parrinello-Rahman scheme and its invariant modification, in which the MD cell with periodic borders is allowed to change in size and shape with time. The main observed path from fee to bce is the Bain transformation, but this process seems to be induced by the tetragonal distortion of the MD cell. Accordingly, the d ynamical trajectory of the transformation does strongly depend on the size and shape of the MD cell and on the MD scheme itself. The unwanted contribu tion from the cell dynamics cannot be eliminated even in the modified schem es based on the Parrinello-Rahman method.