Hyowon Park

Site-selective Mott transition in rare-earth-element nickelates

A combination of density functional and dynamical mean field theory calculations are used to show that the remarkable metal-insulator transition in the rare-earth-element nickelate perovskites arises from a site-selective Mott phase, in which the d electrons on half of the Ni ions are localized to form a fluctuating moment while the d electrons on other Ni ions form a singlet with holes on the surrounding oxygen ions. The calculation reproduces key features observed in the nickelate materials, including an insulating gap in the paramagnetic state, a strong variation of static magnetic moments among Ni sites and an absence of charge order. A connection between structure and insulating behavior is documented. The site-selective Mott transition may be a more broadly applicable concept in the description of correlated materials.

Cluster Dynamical Mean Field Theory of the Mott Transition

We address the nature of the Mott transition in the Hubbard model at half-filling using cluster dynamical mean field theory (DMFT). We compare cluster-DMFT results with those of single-site DMFT. We show that inclusion of the short-range correlations on top of the on-site correlations does not change the order of the transition between the paramagnetic metal and the paramagnetic Mott insulator, which remains first order. However, the short range correlations reduce substantially the critical U and modify the shape of the transition lines. Moreover, they lead to very different physical properties of the metallic and insulating phases near the transition point. Approaching the transition from the metallic side, we find an anomalous metallic state with very low coherence scale. The insulating state is characterized by the narrow Mott gap with pronounced peaks at the gap edge.

Nature of magnetic excitations in superconducting BaFe1.9Ni0.1As2

An outstanding question about the iron-based superconductors has been whether or not their magnetic characteristics are dominated by itinerant or localized magnetic moments. Absolute measurements and calculations of the magnetic response of undoped and Ni-doped BaFe2As2 indicate the latter.

Magnetic excitation spectra in BaFe2As2: a two-particle approach within a combination of the density functional theory and the dynamical mean-field theory method.

We study the magnetic excitation spectra in the paramagnetic state of BaFe

Total energy calculations using DFT+DMFT: Computing the pressure phase diagram of the rare earth nickelates

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Computing total energies in complex materials using charge self-consistent DFT +DMFT

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Coherent band excitations in CePd3: A comparison of neutron scattering and ab initio theory

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Charge transfer across transition-metal oxide interfaces: Emergent conductance and electronic structure

from the \textit{ab initio} perspective. The one-particle excitation spectrum is determined within the combination of the density functional theory and the dynamical mean-field theory method. The two-particle response function is extracted from the local two-particle vertex function, also computed by the dynamical mean field theory, and the polarization function. This method reproduces all the experimentally observed features in inelastic neutron scattering (INS), and relates them to both the one particle excitations and the collective modes. The magnetic excitation dispersion is well accounted for by our theoretical calculation in the paramagnetic state without any broken symmetry, hence nematic order is not needed to explain the INS experimental data.

Failure of DFT-based computations for a stepped-substrate-supported correlated Co wire

A full implementation of the ab initio density functional plus dynamical mean field theory (DFT+DMFT) formalism to perform total energy calculations and structural relaxations is proposed and implemented. The method is applied to the structural and metal-insulator transitions of the rare earth nickelate perovskites as a function of rare earth ion, pressure, and temperature. In contrast to previous DFT and DFT+U theories, the present method accounts for the experimentally observed structure of LaNiO3 and the insulating nature of the other perovskites, and quantitatively reproduces the metal-insulator and structural phase diagram in the plane of pressure and rare earth element. The temperature dependence of the energetics of the phase transformation indicates that the thermal transition is driven by phonon entropy effects.

Origin of doping-induced suppression and reemergence of magnetism in LaFeAsO 1 − x H x

We have formulated and implemented a fully charge self-consistent density functional theory plus dynamical mean-field theory methodology which enables an efficient calculation of the total energy of realistic correlated electron systems. The density functional portion of the calculation uses a planewave basis set within the projector augmented wave method enabling study of systems with large, complex unit cells. The dynamical mean-field portion of the calculation is formulated using maximally localized Wannier functions, enabling a convenient implementation which is independent of the basis set used in the density functional portion of the calculation. The importance of using a correct double-counting term is demonstrated. A generalized form of the standard