Close-packed structures, geometric requirements

Crystal structure is determined by chemical bonds between elementary cells, as well as by the conditions under which the crystal is formed. This paper is focused on bonding-structure relationship in Jahn-Teller (JT) crystals. In simple cases (see below), of several possible crystal structures, the one beneficial for chemical bonding and steric effects actually develops. They determine molecular skeleton of elementary cells, their geometric shape and size. Combined with the requirements of close packing, these are the necessary conditions of growing an ideal crystal with long-range atomic order. 

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