Abstract
Crystalline structures, zone-center phonon modes, and the related dielectric response of the three low-pressure phases of have been investigated in density-functional theory using ultrasoft pseudopotentials and a plane-wave basis. The structures of low-pressure polymorphs are carefully studied with both the local-density approximation (LDA) and the generalized gradient approximation. The fully relaxed structures obtained with either exchange-correlation scheme agree reasonably well with experiment, although LDA yields better overall agreement. After calculating the Born effective charge tensors and the force-constant matrices by finite-difference methods, the lattice dielectric susceptibility tensors for the three phases are computed by decomposing the tensors into the contributions from individual infrared-active phonon modes.
- Received 25 February 2002
DOI:https://doi.org/10.1103/PhysRevB.65.233106
©2002 American Physical Society