Ab initio LDA calculations have been carried out for dopant-related complexes in silicon carbide. Cluster models with localized basis functions are used to calculate spin distributions while supercell calculations are used to determine the relative stabilities as the function of the chemical potential. We show that a divacancy capturing a P atom gives rise to a deep donor level and give an estimate for the occupancy level. Based on the calculated spin distribution on the phosphorus at the Si site next a carbon vacancy (P-Si+V-C), such a complex can indeed be identified with the EPR center "P-V". We show that at high Si/C ratio the formation energy of P at the C site (Pc) and at the Si site is about the same in thermal equilibrium. Pc is also an effective mass donor in 3C-SiC. We have established that the boron substitutional chooses the Si site in a divacancy in both the neutral and the negative charge state, i.e. no bistability occurs. The arising B-Si+V-C complex is a deep acceptor with spin distribution very close to that measured by ENDOR. The acceptor part of the complex is, however the V-C! This explains why the PL spectra finds the acceptor on the same sublattice as N-C.