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

We have calculated the conduction-to-conduction and valence-to-valence absorption spectrum of bound states in $(\mathrm{In},\mathrm{Ga})\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum dots charged with up to three electrons or holes. Several features emerge: (i) In pure (nonalloyed) $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ dots, the $1S\text{\ensuremath{-}}1{P}_{1}$ and $1S\text{\ensuremath{-}}1{P}_{2}$ conduction intraband transitions are fully in-plane polarized along $[1\overline{1}0]$ and [110], respectively, while valence transitions are weakly polarized because the hole $P$ states do not show any in-plane preferential orientation. (ii) In alloyed ${\mathrm{In}}_{0.6}{\mathrm{Ga}}_{0.4}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ dots the [110] and $[1\overline{1}0]$ polarization of the corresponding $1S\text{\ensuremath{-}}1P$ conduction intraband transitions is weakened since the two $1P$ states are mixed by alloy fluctuations. The polarization of valence intraband transitions is insensitive to changes in alloy fluctuations. (iii) For light polarized along [001], we find a strong valence-to-valence transition that involves a weakly confined hole state with predominant light-hole character. (iv) When charging the dots with a few electrons, the conduction intraband transitions display spectroscopic shifts of $\ensuremath{\sim}1\char21{}2\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$. These shifts are a result of correlation effects (captured by configuration interaction) and not well described within the Hartree-Fock approximation. (v) When charging the dots with holes, valence intraband spectra are more complex than the conduction intraband spectra as hole states are strongly affected by spin-orbit coupling, and configuration mixing is more pronounced. Spectroscopic shifts can no longer be identified unambiguously. These predictions could be tested in single-dot spectroscopy of $n$-doped and $p$-doped quantum dots.

Calculation of conduction-to-conduction and valence-to-valence transitions between bound states in (In,Ga)As/GaAs quantum dots

We study the effects of a few types of atomic disorder on the electronic and optical properties of AlAs/GaAs (001) and (111) superlattices: (i) atomic intermixing across the interfaces; (ii) replacing a single monolayer in a superlattice by one containing the opposite atomic type (isoelectronic δ doping); and (iii) random layer‐thickness fluctuations in superlattices (SL). Type (i) is an example of lateral disorder, while types (ii) and (iii) are examples of vertical disorder. Using three‐dimensional empirical pseudopotential theory and a plane‐wave basis, we calculate the band gaps, electronic wave functions, and optical matrix elements for systems containing up to 2000 atoms in the computational unit cell. Spin‐orbit interactions are omitted. Computationally much less costly effective‐mass calculations are used to evaluate the density of states and eigenstates away from the band edges in vertically disordered SLs. Our main findings are: (i) Chemical intermixing across the interface can significantly shi...

Electronic consequences of random layer‐thickness fluctuations in AlAs/GaAs superlattices

A Comment on the Letter by Serdar {umlt O}{breve g}{umlt u}t, James R. Chelikowsky, and Steven G. Louie, Phys.thinspthinspRev.thinspthinspLett.thinspthinsp{bold 79}, 1770 (1997). The authors of the Letter offer a Reply. {copyright} {ital 1999} {ital The American Physical Society}

Comment on "Quantum Confinement and Optical Gaps in Si Nanocrystals"

Simple tests are presented that gauge the accuracy of some of the pseudopotentials currently used in the literature to calculate within the density–functional approach the electronic properties of molecules, solids and surfaces. These include the local ’’soft‐core’’ and ’’hard‐core’’ potentials as well as the nonlocal first principles (’’hard‐core’’) potentials. A discussion of common misconceptions regarding pseudopotentials is included.

Contemporary pseudopotentials—Simple reliability criteria

Application des calculs de pseudopotentiel de premiers principes aux proprietes structurales, aux discontinuites de bande et aux etats electroniques (GaP) n (GaAs) n n≤3. Developpement d'une theorie systematique reliant les niveaux des superreseaux a ceux de leurs constituants en traitant le superreseau dans l'approximation de cristal virtuel. Description semiquantitative des etats de superreseau resultants

Alex Zunger

Papers

Calculation of conduction-to-conduction and valence-to-valence transitions between bound states in (In,Ga)As/GaAs quantum dots

Electronic consequences of random layer‐thickness fluctuations in AlAs/GaAs superlattices

Comment on "Quantum Confinement and Optical Gaps in Si Nanocrystals"

Contemporary pseudopotentials—Simple reliability criteria

First-principles study of intervalley mixing: Ultrathin GaAs/GaP superlattices.