Critical conditions have been determined for intrinsic transformation of a vacancy Frank loop into a stacking fault tetrahedron in a face centered cubic metal by the molecular dynamics method. We found that a stacking fault tetrahedron can be formed from the scalene hexagonal vacancy Frank loops of wide range of sizes due to the dissociation of dislocations. We have also found atomistically the dynamical process in which vacancy and interstitial faulted Frank loops transform into perfect loops by the application of the external shear stress or by raising the temperature. We have determined numerically the critical shear stress and temperature for the initiation of unfaulting. The simulation results clearly unveiled the important role of temperature in the unfaulting mechanism of an interstitial Frank loop. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.