Low Born effective Charges, High Covalency and Strong Optical Activity in $ X_3^{2+} $ Bi $^{3-} $ N $^{3-} $($ X $= Ca, Sr, Ba) $ inverse $-perovskites J Wakini, C Songa, S Chege, FO Saouma, E Wabululu, PW Nyawere, ... arXiv preprint arXiv:2203.00359, 2022 | | 2022 |