  A numerical method for calculation of the electronic structure of transition
metal impurities in semiconductors based on the Green function technique is
developed. The electronic structure of 3d impurity is calculated within the
LDA+U version of density functional method, whereas the host electron Green
function is calculated by using the linearized augmented plane wave expansion.
The method is applied to the Cu impurity in GaP. The results of calculations
are compared with those obtained within the supercell LDA procedure. It is
shown that in the Green function approach Cu impurity has an unfilled 3d shell.
This result paves a way to explanation of the magnetic order in dilute
Ga_{1-x}Cu_xP alloys.
