Using quantum-chemical methods, it has been found that the structure of fluorite coincides with the symmetry and coordination number of central calcium atom in the (O_h)-Ca₇F₁₄ cluster. The Ca–F and F–F interatomic distances in the cluster are 3–4% shorter than in the crystal. The symmetry of the (O_h)–(ScCa₆F₁₄)⁺ cluster mimicking the cationic defect after the β-decay of ⁴⁵Ca does not correspond to the energy minimum. The increase in the cation charge from 1.79 to 2.80 a. u. reduces the radius of the first coordination sphere by 0.14 Å. For ytterbium dihalides, the bond lengths Yb–F 2.344, Yb–Cl 2.897 Å and the cation charges 1.81, 1.64 a. u., respectively, have been found.