  A new formalism to calculate electronic states of vacancies in diamond has
been developed using many-body techniques.This model is based on prevoius
molecular models but does not use configuration interaction and molecular
orbital techniques. A generalized Hubbard Hamiltonian which consists of all
electron-electron interaction terms is calculated on the atomic orbital bases.
Spatial symmetry $T_{d}$ and spin information of system are included in the
form of Hamiltonian, so the eigenstates have automatically the correct spin and
symmetry properties. Optimizing two key parameters of the model that justifies
already reported semi-empirical values can predict accurate values of the
famous absorption lines in neutral and charged vacancies i.e. $GR1$ and $ND1$.
With these parameters the location of the low lying $^{3}T_{1}$ state is 113
mev above the ground state. In addition to these levels whole of the energy
states of the system is predicted. Since the results are obtained without
configuration interaction the model can gives the exact contribution of
electronic configurations in the ground and excited states of the neutral and
charged vacancies. The new results of the model for the ground and excited
states of GR1 are reported.

Materials Science;Strongly Correlated Electrons