Need for a New Metastable State of GaP:O−in the Dean-Henry-Kukimoto Model of GaP: O

The Dean-Henry-Kukimoto model of GaP: O calls for very large lattice relaxation in the transition ${\mathrm{O}}^0$→${\mathrm{O}}^{-}$. We show that spectroscopic data from the transition ${\mathrm{O}}^{+}$→${\mathrm{O}}^0$, augmented with ideas developed by our Green's-function and total-energy calculations, predict a new ${\mathrm{O}}^{-}$ state with very little lattice relaxation and exceedingly weak Ga-O bonds. For this to be compatible with the Dean-Henry-Kukimoto model, the state must be metastable. We cite evidence which supports its existence.