Quasi-vacancy model for impurity centers with partially filled d- and f-shells

It is shown that quasi-vacancy model can be derived using one-electron Green's function method which provides a realistic two-band structure of a semiconductor. This model provides a suitable basis for calculation of the impurity centers which is hard to qualify in terms of purely 'deep' or purely 'shallow' levels, such as impurity centers with partially filled d- and f- shells.