Density-functional-theory calculations have been performed to study the effect of doping and growth stoichiometry on the core structure of a threading edge dislocation in GaN. Four candidate structures were examined and their formation energies were found to depend strongly on Fermi level and growth stoichiometry. A structure having gallium vacancies at the dislocation core is predicted to be most stable inn-type material grown under nitrogen-rich conditions, while a structure without vacancies is most stable inp-type material grown under these conditions. In material grown under gallium-rich conditions, a structure having nitrogen vacancies at the dislocation core is predicted to be most stable inp-type material, whereas a variety of core structures should be present inn-type material. Edge dislocations are predicted to behave as electron traps inn-type material and may act as hole traps inp-type material depending on the growth conditions. ©1998 American Institute of Physics.