First principle calculation of accurate native defect levels in CaF2 Abdelaziz M. Ibraheem, Mohammed A.H. Khalafalla and Mohamed H. Eisa Eur. Phys. J. B, 90 3 (2017) 42 Published online: 08 March 2017 DOI: 10.1140/epjb/e2017-70591-0