Theoretical Prediction of the Structure of InsulatingYH3

Density functional calculations of the total energy have been used to determine minimum energy structures for ${\mathrm{YH}}_3$. Small, symmetry lowering displacements of the hydrogen atoms lead to a structure with an energy which is lower than that of any other structure considered so far and the opening of a large band gap sufficient to explain the recently observed metal-insulator transition in the ${\mathrm{YH}}_x$ system.