Three possible mechanisms for the reconstructive phase transition from the $B1\mathrm{}$ to the $B2\mathrm{}$ structure types are examined: (1) a modified Buerger (MB) pathway, (2) the Watanabe (W) pathway, and (3) a new pathway (T) proposed by Tolédano et al. [Phys. Rev. B 67, 144106 (2003)]. We use first-principles energy calculations to obtain barrier heights for these pathways in NaCl and in PbS. In both NaCl and PbS, the barriers for the MB and T pathways are approximately equal. In NaCl, the barrier for the W pathway is somewhat higher. Both the MB pathway and the T pathway pass through an intermediate $B33\mathrm{}$ structure type. As a result, the fact that a stable B33 intermediate structure is actually observed in PbS does not favor the T pathway over the MB pathway. We also examine experimentally obtained relations between the orientations of the $B1\mathrm{}$ and $B2\mathrm{}$ structures and conclude that they do not definitively favor any pathway over the others.

• Received 20 October 2003

DOI:https://doi.org/10.1103/PhysRevB.69.174111