Methodological aspects of the GW calculation of the carbon vacancy in 3C-SiC

We employ the GW approximation to calculate the properties of the carbon vacancy, a prominent defect in irradiated 3C-SiC. The GW method has been recently proposed for point defects in order to cure the band gap problem of the usual approximations. However, its application relies on stringent approximations, such as the calculation of the relaxation energies of the atomic structures from another simpler approximation, namely the local density approximation. We assess here the validity of this approach in the complex case of the carbon vacancy. Finally, the calculated properties of the carbon vacancy are greatly affected by the use of the GW approximation with respect to earlier studies. The carbon vacancy is a rather shallow donor with a negative U behavior.