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-i nterstitial has been questioned because of the small fine structure term. W e have calculated the spin-spin interaction tensor, which resolves the prob lem, We have also modeled the optical proberties of I-1, and propose an inv ersion-doubling process to give rise to the 6 meV splitting of the ground a nd first excited states. The 1.685 and 1.859 eV lines can then be understoo d as being transitions between states made up from the p-orbitals on the th ree-fold coordinated C atoms. Our calculated piezospectroscopic tensor also agress with experiment.