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Author

A. Wander

Other affiliations: Humboldt State University
Bio: A. Wander is an academic researcher from Daresbury Laboratory. The author has contributed to research in topics: Ab initio & Density functional theory. The author has an hindex of 17, co-authored 31 publications receiving 2083 citations. Previous affiliations of A. Wander include Humboldt State University.

Papers
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TL;DR: In this paper, a hybrid scheme is used to predict the band gaps of a variety of materials, including silicon, and the electronic structure of silicon is examined in some detail and comparisons with alternative theories are made.

771 citations

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TL;DR: In this article, the structure of the polar surfaces of ZnO was studied using ab initio calculations and surface x-ray diffraction and the experimental and theoretical relaxations were in good agreement.
Abstract: The structures of the polar surfaces of ZnO are studied using ab initio calculations and surface x-ray diffraction. The experimental and theoretical relaxations are in good agreement. The polar surfaces are shown to be very stable; the cleavage energy for the (0001)-Zn and (0001;)-O surfaces is 4.0 J/m(2) comparable to 2.32 J/m(2) for the most stable nonpolar (1010) surface. The surfaces are stabilized by an electronic mechanism involving the transfer of 0.17 electrons between them. This leads to 2D metallic surface states, which has implications for the use of the material in gas sensing and catalytic applications.

396 citations

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TL;DR: In this paper, the structure and surface energies of the cleaved, reconstructed, and fully hydroxylated (001) α-quartz surface of various thicknesses are investigated with periodic density functional theory.
Abstract: The structure and surface energies of the cleaved, reconstructed, and fully hydroxylated (001) α-quartz surface of various thicknesses are investigated with periodic density functional theory (DFT). The properties of the cleaved and hydroxylated surface are reproduced with a slab thickness of 18 atomic layers, while a thicker 27-layer slab is necessary for the reconstructed surface. The performance of the hybrid DFT functional B3LYP, using an atomic basis set, is compared with the generalised gradient approximation, PBE, employing plane waves. Both methodologies give similar structures and surface energies for the cleaved and reconstructed surfaces, which validates studying these surfaces with hybrid DFT. However, there is a slight difference between the PBE and B3LYP approach for the geometry of the hydrogen bonded network on the hydroxylated surface. The PBE adsorption energy of CO on a surface silanol site is in good agreement with experimental values, suggesting that this method is more accurate for hydrogen bonded structures than B3LYP. New hybrid functionals, however, yield improved weak interactions. Since these functionals also give superior activation energies, we recommend applying the new functionals to contemporary issues involving the silica surface and adsorbates on this surface.

190 citations

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TL;DR: In this article, the relaxation of the prototypical metal oxide surface, rutile TiO21101 1, has been elucidated using quantitative low-energy electron diffraction using adjustable parameter free selfconsistent phase shifts, which provide a more reliable description of the electron scattering than traditional approaches.
Abstract: The relaxation of the prototypical metal oxide surface, rutile TiO21101 1, has been elucidated using quantitative low-energy electron diffraction. Successful structure determination entailed the development of adjustable parameter free self-consistent phase shifts, which provide a more reliable description of the electron scattering than traditional approaches. The resulting optimized structure is remarkably consistent with that emerging from recent state of the art ab initio calculations. Additionally, the impact of soft surface vibrational modes on the structure determination has been investigated. It was found that the soft surface mode identified in this study has no significant bearing on the interpretation of the LEED-IV data, in contrast to suggestions in the literature.

141 citations

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TL;DR: In this paper, the structure of the ZnO(1010) surface has been determined by using ab initio, all-electron total energy calculations, by employing local basis sets based on Gaussians, and a hybrid density functional (B3LYP).

130 citations


Cited by
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Journal ArticleDOI
TL;DR: This work reexamines the effect of the exchange screening parameter omega on the performance of the Heyd-Scuseria-Ernzerhof (HSE) screened hybrid functional and recommends a new version of HSE with the screened parameter omega=0.11 bohr(-1) for further use.
Abstract: This work reexamines the effect of the exchange screening parameter ω on the performance of the Heyd-Scuseria-Ernzerhof (HSE) screened hybrid functional. We show that variation of the screening parameter influences solid band gaps the most. Other properties such as molecular thermochemistry or lattice constants of solids change little with ω. We recommend a new version of HSE with the screening parameter ω=0.11bohr−1 for further use. Compared to the original implementation, the new parametrization yields better thermochemical results and preserves the good accuracy for band gaps and lattice constants in solids.

4,625 citations

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TL;DR: In this paper, a review of various nanostructures of ZnO grown by the solid-vapour phase technique and their corresponding growth mechanisms is presented. And the application of nanobelts as nanosensors, nanocantilevers, field effect transistors and nanoresonators is demonstrated.
Abstract: Zinc oxide is a unique material that exhibits semiconducting and piezoelectric dual properties. Using a solid–vapour phase thermal sublimation technique, nanocombs, nanorings, nanohelixes/nanosprings, nanobelts, nanowires and nanocages of ZnO have been synthesized under specific growth conditions. These unique nanostructures unambiguously demonstrate that ZnO probably has the richest family of nanostructures among all materials, both in structures and in properties. The nanostructures could have novel applications in optoelectronics, sensors, transducers and biomedical sciences. This article reviews the various nanostructures of ZnO grown by the solid–vapour phase technique and their corresponding growth mechanisms. The application of ZnO nanobelts as nanosensors, nanocantilevers, field effect transistors and nanoresonators is demonstrated.

3,361 citations

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TL;DR: A detailed comparison of the performance of the HSE03 and PBE0 functionals for a set of archetypical solid state systems is presented, indicating that the hybrid functionals indeed often improve the description of these properties, but in several cases the results are not yet on par with standard gradient corrected functionals.
Abstract: Hybrid Fock exchange/density functional theory functionals have shown to be very successful in describing a wide range of molecular properties. For periodic systems, however, the long-range nature of the Fock exchange interaction and the resultant large computational requirements present a major drawback. This is especially true for metallic systems, which require a dense Brillouin zone sampling. Recently, a new hybrid functional [HSE03, J. Heyd, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 118, 8207 (2003)] that addresses this problem within the context of methods that evaluate the Fock exchange in real space was introduced. We discuss the advantages the HSE03 functional brings to methods that rely on a reciprocal space description of the Fock exchange interaction, e.g., all methods that use plane wave basis sets. Furthermore, we present a detailed comparison of the performance of the HSE03 and PBE0 functionals for a set of archetypical solid state systems by calculating lattice parameters, bulk moduli, heats of formation, and band gaps. The results indicate that the hybrid functionals indeed often improve the description of these properties, but in several cases the results are not yet on par with standard gradient corrected functionals. This concerns in particular metallic systems for which the bandwidth and exchange splitting are seriously overestimated.

1,875 citations

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TL;DR: The theoretical modeling of point defects in crystalline materials by means of electronic-structure calculations, with an emphasis on approaches based on density functional theory (DFT), is reviewed in this paper.
Abstract: Point defects and impurities strongly affect the physical properties of materials and have a decisive impact on their performance in applications. First-principles calculations have emerged as a powerful approach that complements experiments and can serve as a predictive tool in the identification and characterization of defects. The theoretical modeling of point defects in crystalline materials by means of electronic-structure calculations, with an emphasis on approaches based on density functional theory (DFT), is reviewed. A general thermodynamic formalism is laid down to investigate the physical properties of point defects independent of the materials class (semiconductors, insulators, and metals), indicating how the relevant thermodynamic quantities, such as formation energy, entropy, and excess volume, can be obtained from electronic structure calculations. Practical aspects such as the supercell approach and efficient strategies to extrapolate to the isolated-defect or dilute limit are discussed. Recent advances in tractable approximations to the exchange-correlation functional ($\mathrm{DFT}+U$, hybrid functionals) and approaches beyond DFT are highlighted. These advances have largely removed the long-standing uncertainty of defect formation energies in semiconductors and insulators due to the failure of standard DFT to reproduce band gaps. Two case studies illustrate how such calculations provide new insight into the physics and role of point defects in real materials.

1,846 citations