(color online) Phase transformation processes at 300 K for an cluster embedded in BCC iron with (a) seven randomly placed nearby vacancies and (b) six randomly placed nearby ⟨110⟩ dumbbells. The atomic projection is in the basal (XY) plane. [(a1) and (b1)] Initial structures; [(a2) and (b2)] structures after relaxation at 0 K; [(a3) and (b3)] states after relaxation at 300 K; [(a4) and (b4)] final structures after full phase transformation. Blue and red spheres indicate iron base atoms and interstitials, respectively. Inserted image in panel (b4) shows the loop structure viewed along the Burgers vector ((1/2)⟨111⟩) direction. The illustrations are obtained with A04 potential.^[20]