Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set

We present ab initio quantum-mechanical molecular-dynamics simulations of the liquid-metal--amorphous-semiconductor transition in Ge. Our simulations are based on (a) finite-temperature density-functional theory of the one-electron states, (b) exact energy minimization and hence calculation of the exact Hellmann-Feynman forces after each molecular-dynamics step using preconditioned conjugate-gradient techniques, (c) accurate nonlocal pseudopotentials, and (d) Nos\'e dynamics for generating a canonical ensemble. This method gives perfect control of the adiabaticity of the electron-ion ensemble and allows us to perform simulations over more than 30 ps. The computer-generated ensemble describes the structural, dynamic, and electronic properties of liquid and amorphous Ge in very good agreement with experiment. The simulation allows us to study in detail the changes in the structure-property relationship through the metal-semiconductor transition. We report a detailed analysis of the local structural properties and their changes induced by an annealing process. The geometrical, bonding, and spectral properties of defects in the disordered tetrahedral network are investigated and compared with experiment.

Ab initio molecular-dynamics simulation of the liquid-metal-amorphous-semiconductor transition in germanium.

The exact density functional for the ground-state energy is strictly self-interaction-free (i.e., orbitals demonstrably do not self-interact), but many approximations to it, including the local-spin-density (LSD) approximation for exchange and correlation, are not. We present two related methods for the self-interaction correction (SIC) of any density functional for the energy; correction of the self-consistent one-electron potenial follows naturally from the variational principle. Both methods are sanctioned by the Hohenberg-Kohn theorem. Although the first method introduces an orbital-dependent single-particle potential, the second involves a local potential as in the Kohn-Sham scheme. We apply the first method to LSD and show that it properly conserves the number content of the exchange-correlation hole, while substantially improving the description of its shape. We apply this method to a number of physical problems, where the uncorrected LSD approach produces systematic errors. We find systematic improvements, qualitative as well as quantitative, from this simple correction. Benefits of SIC in atomic calculations include (i) improved values for the total energy and for the separate exchange and correlation pieces of it, (ii) accurate binding energies of negative ions, which are wrongly unstable in LSD, (iii) more accurate electron densities, (iv) orbital eigenvalues that closely approximate physical removal energies, including relaxation, and (v) correct longrange behavior of the potential and density. It appears that SIC can also remedy the LSD underestimate of the band gaps in insulators (as shown by numerical calculations for the rare-gas solids and CuCl), and the LSD overestimate of the cohesive energies of transition metals. The LSD spin splitting in atomic Ni and $s\ensuremath{-}d$ interconfigurational energies of transition elements are almost unchanged by SIC. We also discuss the admissibility of fractional occupation numbers, and present a parametrization of the electron-gas correlation energy at any density, based on the recent results of Ceperley and Alder.

Self-interaction correction to density-functional approximations for many-electron systems

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

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A comprehensive review of zno materials and devices

High‐Energy Excitonic Transitions in CdSe Quantum Dots.

We report the results of a self-consistent calculation within the local density approximation for all the substitutional 3d transition atom (TA) impurities in an extended silicon host crystal using the quasi band Green's function method. Chemical trends in the gap state energies and 3d-line resonances are discussed as well as trends in the effective electronic configuration of TA impurities. An explanation for the remarkable property that many different charged states of TA impurities exist in the narrow band gap, despite the fact that the corresponding ionized states of the free TA span a range of ∼ 60 eV, is proposed.

Electronic structure of substitutional 3d transition atom impurities in silicon

Recent experiments [1] suggest that the ferromagnetism (FM) in GaAs:Mn is determined by the impurity band rather than holes in the valenceband. We discuss here the physical mechanism of FM mediated by thecarriers in impurity band, where the Mn d-level play a crucial role. Thetheory is based on the ﬁrst principle approach. The paradigm system that combines ferromagnetism (FM) with semicon-ductivity involves Mn (2+) impurity ions substitution for Ga (3+) atoms in GaAs[2, 3, 4, 5, 6, 7]. Such acceptor substitution creates a hole that interacts withthe local moment of d 5 Mn. This doping-induced magnetism could lead to elec-trical control of FM, to the potential beneﬁt of spin-electronics (spintronics).The nature of the ferromagnetism, including its dependence on the hole concen-tration and on that of the Mn ions depends, however, on the physical natureof the hole state. One view -the ”host like hole” model [2, 3, 4, 5] has beenthat the hole resides inside the GaAs valence band. Such view would permitthe use of the language of GaAs semiconductor physics (s-p bonding, extendedwave functions, RKKY exchange) in analyzing the ensuing magnetism and itsdependence on concentration of the relevant species. This scenario, underlyingmost Model Hamiltonian treatments of the problem [3, 5], was inspired by thepreviously known case of isovalent Mn doping of CdTe, where, on account ofthe host metal atom Cd

The Nature of the magnetism-promoting hole state in the prototype magnetic semiconductor

Using first-principles total-energy calculations we identify the microscopic origin and the physical mechanism that leads to light-induced metastability and persistent photoconductivity in the photovoltaic material Cu(In,Ga)Se2 In the presence of photoexcited or electrically injected conduction band electrons, the complex (VSe-VCu) of a Se vacancy with a Cu vacancy is predicted to transform from a shallow electron trap into a deep hole trap upon the persistent capture of two electrons This explains the experimental evidence that for every two holes persistently released to the valence band, one hole trap is generated

Alex Zunger

Papers

High‐Energy Excitonic Transitions in CdSe Quantum Dots.

Electronic structure of substitutional 3d transition atom impurities in silicon

The Nature of the magnetism-promoting hole state in the prototype magnetic semiconductor

Light-induced metastability in Cu(In,Ga)Se2 caused by VSe-VCu complexes

Electronic structure and ferromagnetism of 3d transition metal impurities in GaAs