  The nitrogen-vacancy center in diamond is a promising candidate for realizing
the spin qubits concept in quantum information. Even though this defect is
known for a long time, its electronic structure and other properties have not
yet been explored in detail. We study the properties of the nitrogen-vacancy
center in diamond through density functional theory within the local spin
density approximation, using supercell calculations. While this theory is
strictly applicable for ground state properties, we are able to give an
estimate for the energy sequence of the excited states of this defect. We also
calculate the hyperfine tensors in the ground state. The results clearly show
that: (i) the spin density and the appropriate hyperfine constants are spread
along a plane and unevenly distributed around the core of the defect; (ii) the
measurable hyperfine constants can be found within about 7 A from the vacancy
site. These results have important implications on the decoherence of the
electron spin which is crucial in realizing the spin qubits in diamond.
