First-Principles Study Of The Structural Instabilities In Hexagonal Barium Titanate: Coupling Between The Soft Optical And The Acoustic Modes

Jorge Iniguez, Alberto Garcia, J. M. Perez-Mato

Hexagonal BaTiO_3 undergoes a structural phase transition to an orthorhombic C222_1 phase at T_0 = 222 K. The transition is driven by a soft optical mode with E_2u symmetry whose c…