  A few studies have been recently presented for the existence of oxygen in
diamond, for example, the N3 EPR centres have been theoretically and
experimentally assigned the model made up from complex of substitutional
nitrogen and substitutional oxygen as nearest neighbours. We present ab initio
calculations of substitutional oxygen in diamond in terms of stability,
electronic structures, geometry and hyperfine interaction and show that
substitutional oxygen with C$_{2v}\,$, $S=1$ is the ground state configuration.
We find that oxygen produces either a donor or acceptor level depending on the
position of the Fermi level.
