Oleg E. Peil

Low-energy description of the metal-insulator transition in the rare-earth nickelates

We propose a simple theoretical description of the metal-insulator transition of rare-earth nickelates. The theory involves only two orbitals per nickel site, corresponding to the low-energy antibonding eg states. In the monoclinic insulating state, bond-length disproportionation splits the manifold of eg bands, corresponding to a modulation of the effective on-site energy. We show that, when subject to a local Coulomb repulsion U and Hund’s coupling J , the resulting bond-disproportionated state is a paramagnetic insulator for a wide range of interaction parameters. Furthermore, we find that when U − 3J is small or negative, a spontaneous instability to bond disproportionation takes place for large enough J . This minimal theory emphasizes that a small or negative charge-transfer energy, a large Hund’s coupling, and a strong coupling to bond disproportionation are the key factors underlying the transition. Experimental consequences of this theoretical picture are discussed.

Stacking-fault energy and anti-Invar effect in Fe-Mn alloy from first principles

Based on state-of-the-art density-functional-theory methods we calculate the stacking-fault energy of the prototypical high-Mn steel Fe-22.5 at% Mn between 300 and 800 K. We estimate magnetic thermal excitations by considering longitudinal spin fluctuations. Our results demonstrate that the interplay between the magnetic excitations and the thermal lattice expansion is the main factor determining the anti-Invar effect, the hcp-fcc transformation temperature, and the stacking-fault energy, all of which are in good agreement with measurements.

Approaching finite-temperature phase diagrams of strongly correlated materials: A case study for V2O3

Examining phase stabilities and phase equilibria in strongly correlated materials asks for a next level in the many-body extensions to the local-density approximation (LDA) beyond mainly spectroscopic assessments. Here we put the charge-self-consistent LDA+dynamical mean-field theory (DMFT) methodology based on projected local orbitals for the LDA+DMFT interface and a tailored pseudopotential framework into action in order to address such thermodynamics of realistic strongly correlated systems. Namely a case study for the electronic phase diagram of the well-known prototype Mott-phenomena system V

Self-consistent supercell approach to alloys with local environment effects

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Orbital polarization in strainedLaNiO3: Structural distortions and correlation effects

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Optical spectroscopy and the nature of the insulating state of rare-earth nickelates

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Strong correlations enhanced by charge ordering in highly doped cobaltates.

at higher temperatures is presented. We are able to describe the first-order metal-to-insulator transitions with negative pressure and temperature from the self-consistent computation of the correlated total energy in line with experimental findings.

Impact of antiferromagnetism on the optical properties of rare earth nickelates

We present an efficient and accurate method for calculating electronic structure and related properties of random alloys with a proper treatment of local environment effects. The method is a genera ...

Stability in BCC Transition Metals: Madelung and Band-Energy Effects due to Alloying

Transition-metal heterostructures offer the fascinating possibility of controlling orbital degrees of freedom via strain. Here, we investigate theoretically the degree of orbital polarization that can be induced by epitaxial strain in LaNiO

Configurational thermodynamics of the Fe-Cr sigma phase

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