D. J. Chadi

Bio: D. J. Chadi is an academic researcher from PARC. The author has contributed to research in topics: Pseudopotential & Electronic structure. The author has an hindex of 33, co-authored 68 publications receiving 8067 citations. Previous affiliations of D. J. Chadi include Princeton University.

Special points for Brillouin-zone integrations

Abstract: The efficiency of two different methods for obtaining "special" points useful for Brillouin-zone integrations of periodic functions is compared. We find that for some Bravais lattices (such as body-centered cubic and hexagonal), the method suggested by Monkhorst and Pack leads to different and sometimes less efficient point sets than those previously obtained by Chadi and Cohen. For a two-dimensional oblique lattice, special points twice as efficient as those suggested by Cunningham are given.

Atomic and Electronic Structures of Reconstructed Si(100) Surfaces

Abstract: New structural models for 2\ifmmode\times\else\texttimes\fi{}1 and 4\ifmmode\times\else\texttimes\fi{}2 reconstructed (100) surfaces of Si determined from energy-minimization claculations are presented. The optimal 2\ifmmode\times\else\texttimes\fi{}1 and 4\ifmmode\times\else\texttimes\fi{}2 structures are found to correspond to asymmetric dimer geometries with partially ionic bonds between surface atoms, resulting in semiconducting surface electronic bands. The atomic and electronic structures for the 2\ifmmode\times\else\texttimes\fi{}1 and 4\ifmmode\times\else\texttimes\fi{}2 reconstructed surfaces are discussed.

First-principles study of the atomic reconstructions and energies of Ga- and As-stabilized GaAs(100) surfaces

Abstract: We have carried out ab initio total-energy density-functional calculations to study the reconstructions of GaAs(100) surfaces as a function of Ga and As surface coverage. Equilibrium atomic geometries and energies for Ga- and As-stabilized 1\ifmmode\times\else\texttimes\fi{}1, 2\ifmmode\times\else\texttimes\fi{}1, 1\ifmmode\times\else\texttimes\fi{}2, and 2\ifmmode\times\else\texttimes\fi{}2 surfaces consisting of various combinations of dimers and vacancies were determined. Dimerization of Ga (As) surface atoms is calculated to lower the energy by 1.7 eV (0.7 eV) per dimer and to lead to the most stable atomic configurations. For half-monolayer coverages, relaxation energies are very large, and nondimerized structures are only slightly (0.03--0.05 eV per 1\ifmmode\times\else\texttimes\fi{}1 cell) higher in energy. Asymmetric dimers were tested for As surfaces and found to be higher in energy than symmetric dimers. The stability of surfaces in equilibrium with Ga and As sources is considered and it is shown that the chemical potentials are restricted within limits set by the free energies of the elemental bulk phases of Ga and As. Ab initio calculations of these bulk energies at T=0 K determine the limiting chemical potentials and also the heat of formation, which we find to be 0.73 eV per GaAs pair, compared with the experimental value of 0.74 eV. Our calculations indicate that with excess bulk As available, a full monolayer coverage of As is energetically more favorable than a half-monolayer coverage, whereas with excess Ga available, the surface energy of full and half-monolayer coverages are nearly the same. To examine the effects of larger unit-cell dimensions on total energies, we rely on results from tight-binding calculations. For half-monolayer coverages, 2\ifmmode\times\else\texttimes\fi{}4 unit cells are found to have a significantly lower energy than 2\ifmmode\times\else\texttimes\fi{}2 cells not because of a greater lattice relaxation but because of orbital rehybridization effects which are not possible in a smaller cell. The results of the ab initio and tight-binding calculations indicate that the optimal surface coverage for Ga- and As-terminated surfaces is less than a full monolayer.

Theory of the atomic and electronic structure of DX centers in GaAs and AlxGa1-xAs alloys.

Abstract: We propose that $\mathrm{DX}$ is a negatively charged defect center resulting from the "reaction" $2{d}^{0}\ensuremath{\rightarrow}{d}^{+}+D{X}^{\ensuremath{-}}$ where $d$ represents a substitutional donor. The results of our pseudopotential calculations for Si- and S-induced $\mathrm{DX}$ centers in GaAs indicate large dopant-dependent relaxations leading to threefold-coordinated interstitial sites for either the donor or one of its nearest neighbors. A simple expression for the alloy composition and pressure dependence of the $\mathrm{DX}$ binding energy is suggested and used in an analysis of experimental data.

Spin-orbit splitting in crystalline and compositionally disordered semiconductors

Abstract: The electronic structures of C, Si, Ge, $\ensuremath{\alpha}\ensuremath{-}\mathrm{Sn}$, GaP, GaAs, GaSb, InP, InAs, InSb, and ZnSe are studied using a tight-binding approach which includes spin-orbit interactions. The spin-orbit splittings ${\mathrm{\ensuremath{\Delta}}}_{0}$ and ${\mathrm{\ensuremath{\Delta}}}_{1}$ are related to atomic spin-orbit splittings and optical gaps. The variation of ${\mathrm{\ensuremath{\Delta}}}_{0}$ as a function of chemical composition is studied for a number of alloy systems. It is shown that the nonlinear dependence of ${\mathrm{\ensuremath{\Delta}}}_{0}$ on alloy composition is a disorder-induced effect. The bowing parameter is calculated in terms of tight-binding parameters and band gaps.

Spintronics: Fundamentals and applications

Abstract: Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.

Band parameters for III–V compound semiconductors and their alloys

Abstract: We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

A grid-based Bader analysis algorithm without lattice bias

Abstract: A computational method for partitioning a charge density grid into Bader volumes is presented which is efficient, robust, and scales linearly with the number of grid points. The partitioning algorithm follows the steepest ascent paths along the charge density gradient from grid point to grid point until a charge density maximum is reached. In this paper, we describe how accurate off-lattice ascent paths can be represented with respect to the grid points. This improvement maintains the efficient linear scaling of an earlier version of the algorithm, and eliminates a tendency for the Bader surfaces to be aligned along the grid directions. As the algorithm assigns grid points to charge density maxima, subsequent paths are terminated when they reach previously assigned grid points. It is this grid-based approach which gives the algorithm its efficiency, and allows for the analysis of the large grids generated from plane-wave-based density functional theory calculations.

Electronic Structure: Basic Theory and Practical Methods

Abstract: 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.

First-principles calculations for defects and impurities: Applications to III-nitrides

Abstract: First-principles calculations have evolved from mere aids in explaining and supporting experiments to powerful tools for predicting new materials and their properties. In the first part of this review we describe the state-of-the-art computational methodology for calculating the structure and energetics of point defects and impurities in semiconductors. We will pay particular attention to computational aspects which are unique to defects or impurities, such as how to deal with charge states and how to describe and interpret transition levels. In the second part of the review we will illustrate these capabilities with examples for defects and impurities in nitride semiconductors. Point defects have traditionally been considered to play a major role in wide-band-gap semiconductors, and first-principles calculations have been particularly helpful in elucidating the issues. Specifically, calculations have shown that the unintentional n-type conductivity that has often been observed in as-grown GaN cannot be a...