Refine
Year of publication
- 2005 (193) (remove)
Document Type
- Article (146)
- Doctoral Thesis (40)
- Monograph/Edited Volume (3)
- Habilitation Thesis (2)
- Master's Thesis (1)
- Postprint (1)
Keywords
- 1D (2)
- 2D (2)
- Anthropogene Klimaänderung (2)
- Climate Change (2)
- Integrated Assessment (2)
- Kolloides System (2)
- MHD (2)
- Nanostruktur (2)
- Polyelektrolyt (2)
- Quantendraht (2)
Institute
- Institut für Physik und Astronomie (193) (remove)
In the light of recent intensity-voltage low energy electron diffraction (LEED-IV) experiments [Surf. Sci. 316, 92 (1994); Surf. Rev. Lett. 10, 487 (2003)], the electronic and geometric structure of a water bilayer adsorbed at the Ru(0001) surface are investigated through first-principles total energy calculations, using periodic slab geometries and gradient-corrected density functional theory (DFT). We consider five possible bilayer structures, all roughly consistent with the LEED-IV analysis (three intact structures and two half-dissociated), and a water single layer at Ru(0001). Adsorption energies and substrate-adsorbate geometry parameters are given and discussed in the light of the experiments. We also give a comparative analysis of the electron density redistribution (Delta rho) and of the dipole moment change (Delta mu) induced by water adsorption on the Ru(0001) surface. In agreement with Feibelman [Science 295, 99 (2002)], the half-dissociated structures are found to be more stable than the intact ones, and their adsorption geometries in better agreement with the LEED-IV data. However, the Delta rho analysis shows that a half-dissociated structure induces a Delta mu>0, which would be incompatible with the experimentally measured decrease of the work function following bilayer adsorption; the latter would be consistent, instead, with the Delta mu < 0 induced by the intact structures. It is the aim of this paper to compare various possible adsorption structures, most of them already considered previously, with one and the same method. For this purpose, thick slabs and restrictive computational parameters are chosen to generally address the accuracy and the limits of DFT in reproducing adsorption energies and bond lengths of water-metal interacting systems
This paper is devoted to the digital processing of multicomponent seismograms using wavelet analysis. The goal of this processing is to identify Rayleigh surface elastic waves and determine their properties. A new method for calculating the ellipticity parameters of a wave in the form of a time-frequency spectrum is proposed, which offers wide possibilities for filtering seismic signals in order to suppress or extract the Rayleigh components. A model of dispersion and dissipation of elliptic waves written in terms of wavelet spectra of complex (two-component) signals is also proposed. The model is used to formulate a nonlinear minimization problem that allows for a high-accuracy calculation of the group and phase velocities and the attenuation factor for a propagating elliptic Rayleigh wave. All methods considered in the paper are illustrated with the use of test signals. (c) 2005 Pleiades Publishing, Inc
X-ray diffraction by a crystal in a permanent external electric field : general considerations
(2005)
The variations of X-ray diffraction intensities from a crystal in the presence of a permanent external electric field is modeled analytically using a first-order stationary perturbation theory. The change in a crystal, induced by an external electric field, is separated into two contributions. The first one is related to a pure polarization of an electron subsystem, while the second contribution can be reduced to the displacements of the rigid pseudoatoms from their equilibrium positions. It is shown that a change of the X-ray diffraction intensities mainly originates from the second contribution, while the influence of the pure polarization of a crystal electron subsystem is negligibly small. The quantities restored from an X-ray diffraction experiment in the presence of an external electric field were analyzed in detail in terms of a rigid pseudoatomic model of electron density and harmonic approximation for the atomic thermal motion. Explicit relationships are derived that link the properties of phonon spectra with E-field-induced variations of a structure factor, pseudoatomic displacements and piezoelectric strains. The displacements can be numerically estimated using a model of independent atomic motion if the Debye - Waller factors and pseudoatomic charges are known either from a previous single-crystal X-ray diffraction study or from density functional theory calculations. The above estimations can be used to develop an optimum strategy for a data collection that avoids the measurements of reflections insensitive to the electric-field-induced variations