Stabilization of complex ions by the crystal field: CO 3 2− , NO 3 − , O 3 − , [(OH)4]4−, [(OH)3F]4−, [(OH)2F2]4−

According to Koopmans' theorem, only the electrons associated with molecular levels of negative energy are stable. Many ions which cannot exist in the isolated state because certain occupied levels are positive, become stable in crystals under the stabilization effect arising from the crystal field. As examples, we have studied CO ₃ ^2? in calcite, NO ₃ ^? in NaNO₃, and several natural limpurities: O ₃ ^? in fluorite, [(OH)₄]^4?, [(OH)₃F]^4? and [(OH)₂F₂]^4? in zircon and thorite, by means of the molecular self-consistent field, the crystal field being simulated by point charges. As expected, all the energies corresponding to the occupied levels are negative within the crystal field, contrary to what occurs in the isolated state. Informations concerning the structure and the size of the critical germ are obtained for CaCO₃ and NaNO₃.