First principles study of the of the self-interstitial defect in diamond

First principles techniques have been employed to examine the isolated self-interstitial in diamond. The assignment of the R2 EPR center to the self-interstitial has been questioned because of the small fine structure term. We have calculated the spin-spin interaction tensor, which resolves the problem, We have also modeled the optical proberties of I₁, and propose an inversion-doubling process to give rise to the 6 meV splitting of the ground and first excited states. The 1.685 and 1.859 eV lines can then be understood as being transitions between states made up from the p-orbitals on the three-fold coordinated C atoms. Our calculated piezospectroscopic tensor also agress with experiment.