Abstract
We investigate the temperature-pressure phase diagram of using a first-principles effective-Hamiltonian approach. We find that the zero-point motion of the ions affects the form of the phase diagram dramatically. Specifically, when the zero-point fluctuations are included in the calculations, all the polar (tetragonal, orthorhombic, and rhombohedral) phases of survive down to 0 K, while only the rhombohedral phase does otherwise. This behavior results from a practical equivalence between thermal and quantum fluctuations. Our work confirms the essential correctness of the phase diagram proposed by Ishidate et al. [Phys. Rev. Lett. 78, 2397 (1997)].
- Received 23 April 2002
DOI:https://doi.org/10.1103/PhysRevLett.89.115503
©2002 American Physical Society