Effect of oxygen and zinc vacancies in ferromagnetic C-doped ZnO: Density-functional calculations

•Both the GGA+U and hybrid functional calculations show that two neighboring substitutional C impurities prefer to form nonmagnetic C2 dimer.•Both oxygen and zinc vacancies suppress the ferromagnetism in C-doped ZnO.•Zinc vacancy can even result in antiferromagnetic coupling among C impurities.

The electronic and magnetic properties of pristine and defective ZnO solids, with some O atoms substituted by C, are investigated based on density functional theory. We reveal using the GGA+U and hybrid functional calculations that two neighboring substitutional C impurities prefer to form nonmagnetic C2 dimer. Moreover, our calculations show that both oxygen and zinc vacancies suppress the ferromagnetism in C-doped ZnO and zinc vacancy can even result in antiferromagnetic coupling among C impurities, elucidating the recent experiments.