A first-principles density-functional description of the electronic structures of the high-T c cuprates has remained a long-standing problem since their discovery in 1986, with calculations failing to capture either the insulating (magnetic) state of the pristine compound or the transition from the insulating to metallic state with doping. Here, by taking lanthanum cuprate as an exemplar high-T c cuprate, we show that the recently developed non-empirical, strongly constrained and appropriately normed density functional accurately describes both the antiferromagnetic insulating ground state of the pristine compound and the metallic state of the doped system. Our study yields new insight into the low-energy spectra of cuprates and opens up a pathway toward wide-ranging first-principles investigations of electronic structures of cuprates and other correlated materials.

We show how an accurate first-principles treatment of the antiferromagnetic (AFM) ground state of La2CuO4 can be obtained without invoking any free parameters such as the Hubbard U . The magnitude and orientation of our theoretically predicted magnetic moment of 0.495µB on Cu-sites along the (100) direction are in excellent accord with experimental results. The computed values of the band gap (1.00 eV) and the exchange-coupling (-138 meV) match the corresponding experimental values. We identify interesting band splittings below the Fermi energy, including an appreciable Hund's splitting of 1.25 eV. The magnetic form factor obtained from neutron scattering experiments is also well described by our calculations. Our study opens up a new pathway for first-principles investigations of electronic and atomic structures and phase diagrams of cuprates and other complex materials.arXiv:1808.06283v1 [cond-mat.str-el]

Electrification of heavy-duty transport and aviation requires a paradigm shift in electrode 1 materials and anionic redox represents one possible approach to meeting these demanding targets. However, questions on the validity of the O 2− /O − oxygen redox paradigm remain open and alternative explanations for the origin of the anionic capacity have been proposed because electronic orbitals associated with redox reactions cannot be measured by standard experiments. Here, by using high energy x-ray Compton measurements along with firstprinciples modeling, we show how the electronic orbital that lies at the heart of the reversible and stable anionic redox activity can be imaged and visualized and its character and symmetry can be determined. Differential changes in the Compton profile with Li concentration are shown to be sensitive to the phase of the electronic wave function and carry signatures of electrostatic and covalent bonding effects. Our study not only provides a picture of the workings of a lithium-rich battery at the atomic scale but also suggests pathways for improving existing cathodes and designing new ones.

In the transition metal dichalcogenide IrTe 2 , low-temperature charge-ordered phase transitions involving Ir dimers lead to the occurrence of stripe phases of different periodicities, and nearly degenerate energies. Bulksensitive measurements have shown that, upon cooling, IrTe 2 undergoes two such first-order transitions to (5 × 1 × 5) and (8 × 1 × 8) reconstructed phases at T c 1 ∼ 280 K and T c 2 ∼ 180 K, respectively. Here, using surface sensitive probes of the electronic structure of IrTe 2 , we reveal the first-order phase transition at T c 3 = 165 K to the (6 × 1) stripes phase, previously proposed to be the surface ground state. This is achieved by combining x-ray photoemission spectroscopy and angle-resolved photoemission spectroscopy, which give access to the evolution of stripe domains and a particular surface state, the energy of which is dependent on the Ir dimer length. By performing measurements over a full thermal cycle, we also report the complete hysteresis of all these phases.

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Recent discovery of superconductivity in the doped infinite-layer nickelates has renewed interest in understanding the nature of high-temperature superconductivity more generally. The low-energy electronic structure of the parent compound NdNiO2, the role of electronic correlations in driving superconductivity, and the possible relationship between the cuprates and the nickelates are still open questions. Here, by comparing LaNiO2 and NdNiO2 systematically within a parameter-free, all-electron first-principles density-functional theory framework, we reveal the role of Nd 4f electrons in shaping the ground state of pristine NdNiO2. Strong similarities are found between the electronic structures of LaNiO2 and NdNiO2, except for the effects of the 4f electrons. Hybridization between the Nd 4f and Ni 3d orbitals is shown to significantly modify the Fermi surfaces of various magnetic states. In contrast, the competition between the magnetically ordered phases depends mainly on the gaps in the Ni $$3{d}_{{x}^{2}-{y}^{2}}$$ 3 d x 2 − y 2 band. Our estimated value of the on-site Hubbard U in the nickelates is similar to that in the cuprates, but the value of the Hund’s coupling JH is found to be sensitive to the Nd magnetic moment. In contrast with the cuprates, NdNiO2 presents 3D magnetism with competing antiferromagnetic and (interlayer) ferromagnetic exchange, which may explain why the Tc is lower in the nickelates.

The strongly constrained and appropriately normed (SCAN) semi-local functional for exchangecorrelation is deployed to study the ground-state properties of ternary Heusler alloys transforming martensitically. The calculations are performed for ferromagnetic, ferrimagnetic, and antiferromagnetic phases. Comparisons between SCAN and generalized gradient approximation (GGA) are discussed. We find that SCAN yields smaller lattice parameters and higher magnetic moments compared to the GGA corresponding values for both austenite and martensite phases. Furthermore, in the case of ferromagnetic and non-magnetic Heusler compounds, GGA and SCAN display similar trends in the total energy as a function of lattice constant and tetragonal ratio. However, for some ferrimagnetic Mn-rich Heusler compounds, different magnetic ground states are found within GGA and SCAN.PACS numbers: 71.15. Mb, 71.15.m, 71.20.b, 75.50.y, 81.30.Kf arXiv:1901.09460v1 [cond-mat.mtrl-sci]

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