Van der Waals interactions in ionic and semiconductor solids

in Physical Review Letters (2011), 107(24),

Van der Waals (vdW) energy corrected density-functional theory is applied to study the cohesive properties of ionic and semiconductor solids (C, Si, Ge, GaAs, NaCl, and MgO). The required polarizability ... [more ▼]

Van der Waals (vdW) energy corrected density-functional theory is applied to study the cohesive properties of ionic and semiconductor solids (C, Si, Ge, GaAs, NaCl, and MgO). The required polarizability and dispersion coefficients are calculated using the dielectric function obtained from time-dependent density-functional theory. Coefficients for "atoms in the solid" are then calculated from the Hirshfeld partitioning of the electron density. It is shown that the Clausius-Mossotti equation that relates the polarizability and the dielectric function is accurate even for covalently-bonded semiconductors. We find an overall improvement in the cohesive properties of Si, Ge, GaAs, NaCl, and MgO, when vdW interactions are included on top of the Perdew-Burke- Ernzerhof or Heyd-Scuseria-Ernzerhof functionals. The relevance of our findings for other solids is discussed. © 2011 American Physical Society. [less ▲]

van der Waals Interactions in Material Modelling

in Handbook of Materials Modeling: Methods: Theory and Modeling (2018)

Van der Waals (vdW) interactions stem from electronic zero-point fluctuations and are often critical for the correct description of structure, stability, and response properties of molecules and materials ... [more ▼]

Van der Waals (vdW) interactions stem from electronic zero-point fluctuations and are often critical for the correct description of structure, stability, and response properties of molecules and materials, including biomolecules, nanomaterials, and material interfaces. Here, we give a conceptual as well as mathematical overview of the current state of modeling vdW interactions,focusing in particular on the consequences of different approximations for practical applications. We present a systematic classification of approximate first-principles models based on the adiabatic-connection fluctuation-dissipation theorem, namely the nonlocal density functionals, interatomic methods, and methods based on the random-phase approximation. The applicability of these methods to different types of materials and material properties is discussed in connection with availability of theoretical and experimental benchmarks. We conclude with a roadmap of the open problems that remain to be solved to construct a universal, efficient, and accurate vdW model for realistic material modeling. [less ▲]

Van parochiezaal tot wereldnetwerk: 25 jaar C.V. Varkenszorg

Book published by Centrum voor Agrarische Geschiedenis (2012)

Vanishing gap in LiF for electronic excitations by slow antiprotons

in Physical Review. B (2009), 79(12),

We study the influence of antiprotons and protons traveling through LiF on the band structure of the insulator using the embedded-cluster method. The crystal is represented by F(m)(-)Li(n)(+) clusters ... [more ▼]

We study the influence of antiprotons and protons traveling through LiF on the band structure of the insulator using the embedded-cluster method. The crystal is represented by F(m)(-)Li(n)(+) clusters with up to 19 fluorine ions embedded in a lattice of point charges representing the remainder of the crystal. The minimum excitation energy of LiF perturbed by the (anti)proton impurity is calculated employing the multiconfiguration self-consistent field method. The repulsive potential of the antiproton causes a dramatic local perturbation of the LiF band structure. We find a strong suppression of the excitation energy by more than an order of magnitude compared to that of the unperturbed crystal. The present results provide a simple explanation of recent stopping-power experiments for antiprotons in LiF which, surprisingly, found a "metal-like" behavior of the wide-band-gap insulator LiF. Our results also agree with recent experimental data indicating a deviation from metallic behavior of the stopping power of proton projectiles. [less ▲]

Vapour phase alkali species for Cu(In,Ga)Se2 solar cells

Scientific Conference (2015, September)

Alkalis are essential in Cu(In,Ga)Se2 absorber layers for efficient solar cells. Current doping methods rely on solid state diffusion of an alkali through to the absorber layer, e.g. a thin NaF layer on ... [more ▼]

Alkalis are essential in Cu(In,Ga)Se2 absorber layers for efficient solar cells. Current doping methods rely on solid state diffusion of an alkali through to the absorber layer, e.g. a thin NaF layer on Mo or NaCl dissolved in a metal precursor ink[1]. The apparent concentration of alkali in the final absorber is determined by the initial alkali dosing and the use of an interfacial barrier to stop alkali diffusion from the substrate. Until now the vapor–absorber interface as a source or sink of alkali doping has been largely ignored. We show that device efficiency improves from 2 to 8% by gas phase Na adsorption alone. Conversely initial results show that Na can also be desorbed to the gas phase. Although these efficiencies are lower than those obtained by including Na directly in the precursor (device efficiency 13.3% [1]), the findings are relevant to all chalcogenide growers as they show that exact doping, and thus control of device efficiency, is only possible when gas phase adsorption/desorption processes are controlled. [less ▲]

Varadhan estimates for diffusions with time dependent coefficients

in Huskova, Marie; Lachout, Petr; Visek, Jan Amos (Eds.) Proceedings of Prague Stochastics 98 (1998)

Varia

in Flux: Cahiers Scientifiques Internationaux Réseaux et Territoires (2021), 123

Numéro Varia de Flux coordonné par C. Henriot et V. Schafer

Varia

in Flux: Cahiers Scientifiques Internationaux Réseaux et Territoires (2018), 113(3), 121

Au-delà de la diversité des thématiques, espaces et temporalités appréhendés et des méthodologies choisies, les auteurs de ces six Varia partagent, outre leur intérêt pour les territoires, les acteurs et ... [more ▼]

Au-delà de la diversité des thématiques, espaces et temporalités appréhendés et des méthodologies choisies, les auteurs de ces six Varia partagent, outre leur intérêt pour les territoires, les acteurs et le souhait d’analyser finement les outils, débats et enjeux à l’œuvre, un intérêt pour les trajectoires, qu’elles soient décisionnelles et s’appréhendent en termes de gouvernance, ou matérielles et se lisent en termes d’infrastructures. [less ▲]

A Variability Perspective of Mutation Analysis

in Proceedings of the 22nd ACM SIGSOFT International Symposium on the Foundations of Software Engineering (FSE 2014) (2014)

VARIABILITY-DRIVEN DESIGN CONFIGURATOR OF SPACE SYSTEMS TO SUPPORT DECISION-MAKERS

Scientific Conference (2022, October)