First-principles investigation of the ferroelectric instability in KH2PO4

S. KOVAL; J. KOHANOFF; R. L. MIGONI; A. BUSSMANN-HOLDER

Schwabisch Gmund

Conferencia; Psi-k2000 conference on Ab initio Calculations; 2000

Abstract:The origin of ferroelectricity in KH2PO4 (KDP) is studied by first-principles electronic structure calculations. In the low-temperature phase, the collective off-centre ordering of the protons is accompanied by an electronic charge delocalization from the near and localization at the far oxygen within the O–H⋯O bonds. Electrostatic forces, then, push the K+ ions towards off-centre positions, and induce a macroscopic polarization. The analysis of the correlation between different geometrical and electronic quantities, in connection with experimental data, supports the idea that the role of tunnelling in isotopic effects is irrelevant. Instead, geometrical quantum effects appear to play a central role.