There is an increasing interest in the investigation of defects formation and properties in multiferroics, as they are believed to play a key role in enhancing transport properties [1,2] (to the point of superconductivity in WO3 [3]), or creating new complex distribution of the magnetic/electric degrees of freedom (e.g. vortices [4]). The impact of defects on pinning domain walls [5,6], fatigue and imprint, remains to be exhaustively studied in order to understand how defects can deteriorate/enhance material functionalities. We studied the occurrence of single and bi-defects in Bismuth Ferrite using ab-initio calculation with ABINIT, both in GGA and LDA+U, and show that the necessary corrections to achieve the study of defects in the dilute limit yield similar results. In addition, we show that single point defects will tend to aggregate, with a binding energy for the Bi-O pair of approximately 0.15 eV. Finally, we study the possibility to engineer defects by using different atmospheres in oxygen. Acknowledgements References [1] S. Farokhipoor, B. Noheda, Phys. Rev. Lett. 107, 127601, (2011). [2] J. Seidel, L. Martin, Q. He et al., Nat. Mat. 8, 229, (2009). [3] E. Salje, Chem Phys Chem 11, 940, (2010). [4] D. Viehland and E. Salje, Adv. Phys. 63, 267, (2014). [5] L. He and D. Vanderbilt, Phys. Rev. B 68, 134103 (2003) [6] A. Chandrasekaran et al., Phys. Rev. B 88, 214116 (2013)