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

Stability of atomic and diatomic hydrogen in fcc palladium

Using the first‐principles pseudopotential method we have studied the fully covered cation‐terminated (001) surfaces of Ga0.5In0.5P alloys. We find that among several possible Ga and In surface patterns (within a 2×2 unit cell), the one corresponding to CuPt‐like bulk ordering is stabilized by ∼100 meV per surface atom. This structure has been observed experimentally in thick films, yet is known to be bulk unstable. The stability of a CuPt‐like surface layer is related to electronically driven surface reconstructions—dimerization, buckling, and tilting—which are discussed in detail.

Surface reconstructions and surface energies of monolayer‐coverage cation‐terminated Ga0.5In0.5P(001) surfaces

Erratum: Room-Temperature Ferromagnetism in Mn-Doped Semiconducting CdGeP 2 [Phys. Rev. Lett. 88, 047205 (2002)]

Coherently strained GaX/InX interfaces (X=P, Sb) lattice matched to a (001)-oriented substrate are predicted to have a type-I band-gap alignment, with both the valence-band maximum and the conduction-band minimum (CBM) located on the In-rich material. At the same time, the CBM wave function of short-period (GaX${)}_{\mathit{n}}$/(InX${)}_{\mathit{n}}$ superlattices is predicted to have larger amplitude on the GaX layers, leading to a type-II alignment. We show that (i) a type-II\ensuremath{\rightarrow}type-I transition occurs around the period n=4; (ii) this transition has a different origin with respect to the well-known case of GaAs/AlAs superlattices; (iii) the band structure of ultrathin superlattices cannot be explained in terms of a simple effective-mass theory; (iv) the wave-function localization in short-period superlattices is determined by the atomic orbital energies.

Type-II-->type-I transition in (GaX)n/(InX)n (001) superlattices (X=P, Sb) as a function of period n.

Spontaneous CuPt-like ordering in III-V alloys causes an anisotropy in the intensities of the transitions between the split valence-band maximum states and the conduction-band minimum. This optical anisotropy has been detected in ordered III-V alloys using modulated reflectivity, and more recently, using reflectance-difference spectroscopy (RDS). We derive here a general formula relating the ordering-induced bulk RDS intensity with the degree of long-range order. We show that the previously neglected coupling between the spin-orbit split-off band and the crystal-field split-off band is crucial for determining the RDS intensity of the Ga{sub {ital x}}In{sub 1{minus}{ital x}}P alloy.

Alex Zunger

Papers

Stability of atomic and diatomic hydrogen in fcc palladium

Surface reconstructions and surface energies of monolayer‐coverage cation‐terminated Ga0.5In0.5P(001) surfaces

Erratum: Room-Temperature Ferromagnetism in Mn-Doped Semiconducting CdGeP 2 [Phys. Rev. Lett. 88, 047205 (2002)]

Type-II-->type-I transition in (GaX)n/(InX)n (001) superlattices (X=P, Sb) as a function of period n.

Theory of reflectance-difference spectroscopy in ordered III-V semiconductor alloys