The mechanism of the $B3/B1\mathrm{}$ phase transition of SiC has been investigated by periodic LCAO-DFT least-enthalpy calculations. A new transformation pathway, based on a $\mathrm{Pmm}2\mathrm{}$ orthorhombic intermediate state with two SiC units per cell, is found to be energetically favored over the traditional $R3m$ mechanism. The computed activation enthalpy is 0.75 eV/SiC unit at the predicted transition pressure of 92 GPa ( $B3\mathrm{LYP}$ functional). Activation enthalpy and activation volume vs pressure are analyzed to characterize the kinetic aspects of the transformation.

• Received 20 March 2001

DOI:https://doi.org/10.1103/PhysRevLett.87.035504