Crystal Structure of β-La₂Mo₂O₉ from First Principles Calculation

Arrangements of O ions in β-La₂Mo₂O₉ are studied by first principles calculation with two different calculation schemes. All final structure configurations consist of MoO₄-tetrahedra, MoO₅-hexahedra, LaO₈ and LaO₇ polyhedra. Molybdenum polyhedra are isolated from each other, lanthanum polyhedra are connected together by sharing O ions. The occupancies of three crystallographic distinct O sites O(1), O(2) and O(3) are 100%, 91.7% and 25%, respectively, consistent with experiments. All configurations are related to each other by one of 12 symmetry operations of P2₁3 space group, suggesting that the structure observed experimentally may be interpreted as a time and spatial average of these local or inherent structures.