First Principles Calculations Using Linear Response Theory for Ferroelectrics

摘要

First principles density functional methods using LAPW and LAPW linear responsemethod were applied to study the incipient ferroelectric SrTiO3. Despite similarities to BaTiO3, SrTiO3 remains paraelectric down to zero temperature, transforming instead to an antiferrodistortive structure at 105 K. As a function of wavevector, the linear response calculations show structural instabilities along the R-M-R line in the Brillouin zone, consistent with this antiferrodistortive ground state. Although a ferroelectric type instability was also found near the zone center as in BaTiO3, the phase space of this instability is greatly reduced by comparison. Moreover, we find that the antiferrodistortive phase is stable, marginally, against ferroelectric structural distortions. In combination, these findings help explain the absence of a transition to a ferroelectric structure.