2017, Vol.20, No.3, pp. 216-227
In the present paper one of Nb,Ta,Ti-oxide minerals, namely CaNb2O6 crystal, is considered. This crystal has complicated structure with the unit cell containing 34 atoms. It is shown that this crystal can be described with the help of several simple building blocks, each containing four atoms, one oxygen anion and three (fractional) cations. These building blocks help one to describe crystal geometry and, in particular, to generate various stoichiometric clusters in the crystal. The building blocks are useful also in the crystal electronic structure description. The stoichiometric cluster containing 58 atoms was generated to represent the CaNb2O6 crystal. This cluster electronic structure was calculated with the embedding potential method. It was found that orbitals, which are localized on a building block and written in the building block atomic basis set only, are good approximation to the noncanonical valence occupied orbitals in the CaNb2O6 crystal. The directed . and . orbitals were calculated to represent the O–Nb bonds in the CaNb2O6 crystal. At the same time, no orbital was found, which can be considered as O–Ca bond orbital..
Key words: crystal electronic structure, embedding, localized orbitals
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