Abstract
Rare-earth nickelates exhibit a metal–insulator transition accompanied by a structural distortion that breaks the symmetry between formerly equivalent Ni sites. The quantitative theoretical description of this coupled electronic–structural instability is extremely challenging. Here, we address this issue by simultaneously taking into account both structural and electronic degrees of freedom using a charge self-consistent combination of density functional theory and dynamical mean-field theory, together with screened interaction parameters obtained from the constrained random phase approximation. Our total energy calculations show that the coupling to an electronic instability toward a charge disproportionated insulating state is crucial to stabilize the structural distortion, leading to a clear first order character of the coupled transition. The decreasing octahedral rotations across the series suppress this electronic instability and simultaneously increase the screening of the effective Coulomb interaction, thus weakening the correlation effects responsible for the metal–insulator transition. Our approach allows to obtain accurate values for the structural distortion and thus facilitates a comprehensive understanding, both qualitatively and quantitatively, of the complex interplay between structural properties and electronic correlation effects across the nickelate series.
Highlights
The mode decomposition allows for a clear conceptional distinction between different structural degrees of freedom, which enables us to obtain those structural degrees of freedom for which correlation effects are not crucial from standard DFT calculations, while the important breathing mode distortion is obtained from DFT + DMFT total energy calculations
The Wannier functions are used as localized basis orbitals to construct the effective impurity problems for our fully charge self-consistent (CSC) DFT + DMFT calculations,[34] where the long bond (LB) and short bond (SB) Ni sites are treated as two separate impurity problems coupled through the DFT + DMFT self-consistency loop, and the system is constrained to remain paramagnetic
In summary, the successful application of CSC DFT + DMFT and symmetry-based mode analysis, without ad hoc assumptions regarding the strength of the Hubbard interaction or fixing the 20 atom Pbnm unit cell
Summary
Complex transition metal oxides exhibit a variety of phenomena, such as, e.g., multiferroicity,[1] non-Fermi liquid behavior,[2] hightemperature superconductivity,[3] or metal–insulator transitions (MIT),[4] which are very intriguing, but are of high interest for future technological applications.[5,6,7] the quantitative predictive description of these materials and their properties represents a major challenge for modern computational materials science, due to the importance of electronic correlation effects as well as due to the intimate coupling between electronic, magnetic, and structural degrees of freedom.[4,8]. Due to challenges in synthesis, experimental data on the bulk materials is relatively sparse, and quantitative predictive calculations are highly valuable to gain a better understanding of the underlying mechanisms
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