Atomistic simulations of the incipient ferroelectric KTaO${}_3$

A parameterized effective Hamiltonian approach is used to investigate KTaO${}_3$. We find that the experimentally observed anomalous dielectric response of this incipient ferroelectric is well reproduced by this approach, once quantum effects are accounted for. Quantum fluctuations suppress the paraelectric–to–ferroelectric phase transition; it is unnecessary to introduce defects to explain the dielectric behavior. The resulting quantum-induced local structure exhibits off-center atomic displacements that display {\sl longitudinal, needle-like correlations} extending a few lattice constants.