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

• DFT calculations were utilized to analyze bonds in YMnO3 in both PE and FE phases.
• Both non-magnetic and antiferromagnetic order of Mn moments was taken into account.
• Band gap and electronic structure agree well with experimental findings.
• Enhanced hybridization between Y dz2 and O pz orbital was noted in the FE phase.
• Origin of ferroelectric distortion in YMnO3 can be described by Y d0-ness model.

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 4dz2 and the O pz orbitals. The results from present study, therefore, substantiate the Y d0-ness model to explain ferroelectric distortion in hexagonal manganites.