The generalization of the Local Density Approximation (LDA) method for the systems with strong Coulomb correlations is presented which gives a correct description of the Mott insulators. The LDA+U method is based on the model hamiltonian approach and allows to take into account the non-sphericity of the Coulomb and exchange interactions. parameters. Orbital-dependent LDA+U potential gives correct orbital polarization and corresponding Jahn-Teller distortion. To calculate the spectra of the strongly correlated systems the impurity Anderson model should be solved with a many-electron trial wave function. All parameters of the many-electron hamiltonian are taken from LDA+U calculations. The method was applied to NiO and has shown good agreement with experimental photoemission spectra and with the oxygen Kα X-ray emission spectrum.

https://iopscience.iop.org/article/10.1088/0953-8984/9/4/002/pdf

First-principles calculations of the electronic structure and spectra of strongly correlated systems: the LDA+ U method

Multiferroic magnetoelectrics are materials that are both ferromagnetic and ferroelectric in the same phase. As a result, they have a spontaneous magnetization that can be switched by an applied magnetic field, a spontaneous polarization that can be switched by an applied electric field, and often some coupling between the two. Very few exist in nature or have been synthesized in the laboratory. In this paper, we explore the fundamental physics behind the scarcity of ferromagnetic ferroelectric coexistence. In addition, we examine the properties of some known magnetically ordered ferroelectric materials. We find that, in general, the transition metal d electrons, which are essential for magnetism, reduce the tendency for off-center ferroelectric distortion. Consequently, an additional electronic or structural driving force must be present for ferromagnetism and ferroelectricity to occur simultaneously.

Why Are There so Few Magnetic Ferroelectrics

Preface Acknowledgements Notation Part I. Overview and Background Topics: 1. Introduction 2. Overview 3. Theoretical background 4. Periodic solids and electron bands 5. Uniform electron gas and simple metals Part II. Density Functional Theory: 6. Density functional theory: foundations 7. The Kohn-Sham ansatz 8. Functionals for exchange and correlation 9. Solving the Kohn-Sham equations Part III. Important Preliminaries on Atoms: 10. Electronic structure of atoms 11. Pseudopotentials Part IV. Determination of Electronic Structure, The Three Basic Methods: 12. Plane waves and grids: basics 13. Plane waves and grids: full calculations 14. Localized orbitals: tight binding 15. Localized orbitals: full calculations 16. Augmented functions: APW, KKR, MTO 17. Augmented functions: linear methods Part V. Predicting Properties of Matter from Electronic Structure - Recent Developments: 18. Quantum molecular dynamics (QMD) 19. Response functions: photons, magnons ... 20. Excitation spectra and optical properties 21. Wannier functions 22. Polarization, localization and Berry's phases 23. Locality and linear scaling O (N) methods 24. Where to find more Appendixes References Index.

Electronic Structure: Basic Theory and Practical Methods

Full-potential, linearized augmented plane wave programs for crystalline systems

We present a review of the basic ideas and techniques of the spectral density functional theory which are currently used in electronic structure calculations of strongly{correlated materials where the one{electron description breaks down. We illustrate the method with several examples where interactions play a dominant role: systems near metal{insulator transition, systems near volume collapse transition, and systems with local moments.

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Electronic structure calculations with dynamical mean-field theory

We would like to improve our understanding of the behaviour of real solids. Why do atoms combine into molecules and solids in the way they do and what is the response of these aggregates of atoms to external fields, stress, temperature, etc. ? Answers to such questions would, for instance, be a useful guide in our, so far mostly empirical, search for new and better materials Stronger materials, materials which corrode less, better catalysts, better magnets, better semi- or superconductors, and, materials with properties unknown today. I expect that future advances in this field will be aided by insight obtained from calculations of the electronic structure.

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Linear methods in band theory

We give a complete description of a relativistic augmented-plane-wave calculation of the band structures of the paramagnetic fcc transition metals Ir, Rh, Pt, and Pd. The width and position of the $d$ band decrease in the sequence Ir, Pt, Rh, Pd; and $N({E}_{F})=13.8,23.2,18.7, \mathrm{and} 32.7$ (states/atom)/Ry, respectively. Spin-orbit coupling is important for all four metals and the coupling parameter varies by 30% over the $d$ bandwidth. Detailed comparisons with de Haas---van Alphen Fermi-surface dimensions have previously been presented and the agreement was very good. Comparison with measured electronic specific-heat coefficients $\ensuremath{\gamma}$ and cyclotron masses indicate that the average mass enhancements are 1.37, 1.44, 1.63, and 1.66 for Ir, Rh, Pt, and Pd, respectively; and that for both Pt and Pd the partial enhancements on the closed electron surface and on the open hole surface are 1.51 and 1.68, respectively. Saddle points in the fifth band are important for the large peak in $N(E)$ near the top of the $d$ band. The experimental $\ensuremath{\gamma}(x)$ for ${\mathrm{Rh}}_{x}{\mathrm{Pd}}_{1\ensuremath{-}x}$ is not uniformly enhanced over the calculated rigid-band $\ensuremath{\gamma}(x)$. The experimentally observed field and temperature dependences of the magnetic susceptibility for Pd are consistent with the calculated $N(E)$.

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Electronic Structure of the fcc Transition Metals Ir, Rh, Pt, and Pd

Using the linear muffin-tin-orbital method described in the previous paper, (Phys. Rev. B 12: 3060) the electronic structures of the hcp transition metals, Zr, Hf, Ru, and Os were calculated . It is shown how the band structures of these metals may be synthesized from the sp and d bands, and the effects of hybridization, relativistic band shifts and spin--orbit coupling are illustrated by the example of Os. By making use of parameters derived from the muffin-tin potential, trends in the positions and widths of the energy bands, especially the d bands, are discussed as a function of the location in the periodic table. The densities of states of the four metals are presented and the calculated heat capacities compared with experiment. The Fermi surfaces of both Ru and Os are found to be in excellent quantitative agreement with de Haas--van Alphen measurements, indicating that the calculated d-band position is misplaced by less than 10 mRy. Very small pieces of Fermi surface, which have not yet been observed experimentally, are predicted for Os. The limited amount of experimental information available for Zr can be fairly satisfactorily interpreted if the calculated d bands, are raised by about 10--20 mRy relative tomore » the sp bands. This gives rise to a Fermi surface which is topologically equivalent to that recently found in Ti, and which does not support open orbits when the magmetic field is sufficiently great that breakdown is complete. It is suggested that the Fermi surface of Hf is probably similar, although very little experimental evidence is available for this metal. Some comments are made about the calculational method, which has proved to be physically transparent, accurate and extremely fast, and the adequancy of the standard potential, which has now been successfully employed in calculations on the great majority of the transition metals. (auth)« less

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O. Krogh Andersen

Papers

Linear methods in band theory

Electronic Structure of the fcc Transition Metals Ir, Rh, Pt, and Pd

Electronic structure of hcp transition metals