The energy band structures of MgO, LiF, and NaF are calculated by the LMTO method with a set of different atomic spheres radii. It is shown that MgO is distinct from fluorides in that a pure ionic charge distribution is not achieved. Such a behaviour of the electron density is explained by the presence of a potential barier inside the oxygen atomic sphere near its boundary. As a consequence the charge configuration of MgO is suggested to be close to Mg2+O− plus one electron distributed in the interionic region.

Calculations are made for clusters simulating the Vk‐center in NaF and a hypothetic self‐trapped hole in MgO within the embedded cluster approach. The “non‐ionic” charge configuration of MgO, described earlier, is analysed as a possible cause of the absence of the hole self‐trapping manifestations in the oxide according to the mechanism known for NaF. Due to the delocalization of oxygen 2p‐states the hole orbital is oriented, in contrast to NaF, perpendicularly to the 2‐anion quasi‐molecule axis, while the hole state itself lies close to the top of the potential barrier bonding this state.

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The electronic structure of CaO and SrO in the ground state is calculated in terms of the crystalline cluster approach. Calculations for 27‐atom clusters at different ratios between muffin‐tin sphere radii show that in both crystals the charge configuration is similar to that obtained earlier for MgO: Mg2+ ‐O− plus one electron, distributed in the interstitial region. Such distribution of the electronic density is interpreted in terms of the theory of resonance scattering on the anion effective potential.

In order to be useful for ionic crystals cluster calculations must be modified so as to simulate the crystal potential in a reasonable way. Two aspects of such calculations-the normalization of the orbitals and the construction of the coulomb potential-are analyzed in some detail. Illustrative calculations are camed out for MgO and the results are compared with experimental data and with other theoretical results.