Analysis of the Mn-O and Y-O bonds in paraelectric and ferroelectric phase of magnetoelectric YMnO3 from the first principles calculations

We report the first-principles band-structure calculations on multiferroic hexagonal YMnO3, realized with objective to study how the Mn-O and Y-O bonds change when the compound undergoes paraelectric (PE) <-> ferroelectric (FE) phase transition. The compound was simulated in non-magnetic and antiferromagnetic configuration. Exchange-correlation effects were treated by modified Becke-Johnson approach, which enabled successful reproduction of experimental band gap in the FE phase and predicted a small band gap in the PE phase, in agreement with experimental findings. The Mn-O and Y-O bonds were investigated qualitatively, by inspecting charge density maps projected onto suitable planes, and quantitatively, by applying the Bader's topological analysis and comparing electronic densities of states in different phases. Independently of the fact how the Mn ions were treated, as spin-polarized or not, the results indicate that the Mn-O bonds do not suffer significant changes during the PE-FE phase transition, while the Y-O bonds become more covalent, with clear signs of hybridization between Y 4d(z)(2) and the O p(z) orbitals. The results from present study, therefore, substantiate the Y d(0)-ness model to explain ferroelectric distortion in hexagonal manganites. (C) 2015 Elsevier B.V. All rights reserved.