Density-functional study of hydrogen chemisorption on vicinal Si(001) surfaces

Relaxed atomic geometries and chemisorption energies have been calculated for the dissociative adsorption of molecular hydrogen on vicinal Si(001) surfaces. We employ density-functional theory, together with a pseudopotential for Si, and apply the generalized gradient approximation by Perdew and Wang to the exchange-correlation functional. We find the double-atomic-height rebonded D_B step, which is known to be stable on the clean surface, to remain stable on partially hydrogen-covered surfaces. The H atoms preferentially bind to the Si atoms at the rebonded step edge, with a chemisorption energy difference with respect to the terrace sites of >sim 0.1 eV. A surface with rebonded single atomic height S_A and S_B steps gives very similar results. The interaction between H-Si-Si-H mono-hydride units is shown to be unimportant for the calculation of the step-edge hydrogen-occupation. Our results confirm the interpretation and results of the recent H_2 adsorption experiments on vicinal Si surfaces by Raschke and Hoefer described in the preceding paper.Comment: 13 pages, 8 figures, submitted to Phys. Rev. B. Other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm

Electron penetration in the nucleus and its effect on the quadrupole interaction

A series expansion of the interaction between a nucleus and its surrounding electron distribution provides terms that are well-known in the study of hyperfine interactions: the familiar quadrupole interaction and the less familiar hexadecapole interaction. If the penetration of electrons into the nucleus is taken into account, various corrections to these multipole interactions appear. The best known one is a scalar correction related to the isotope shift and the isomer shift. This paper discusses a related tensor correction, which modifies the quadrupole interaction if electrons penetrate the nucleus: the quadrupole shift. We describe the mathematical formalism and provide first-principles calculations of the quadrupole shift for a large set of solids. Fully relativistic calculations that explicitly take a finite nucleus into account turn out to be mandatory. Our analysis shows that the quadrupole shift becomes appreciably large for heavy elements. Implications for experimental high-precision studies of quadrupole interactions and quadrupole moment ratios are discussed. A literature review of other small quadrupole-like effects is presented as well

Improved L(2)-stabilization theory to compute resonances under multichannel conditions

Salzgeber RF, Manthe U, Weiss T, Schlier C. Improved L(2)-stabilization theory to compute resonances under multichannel conditions. CHEMICAL PHYSICS LETTERS. 1996;249(3-4):237-243

Validation of the Hamilton Program for Schizophrenia Voices Questionnaire: associations with emotional distress and wellbeing and invariance across diagnosis and sex

Background: Voice-hearing is a transdiagnostic experience with an evident negative impact on patients. Good quality measurement is needed to further elucidate the nature, impact and treatment of voice-hearing experiences across patient groups. The Hamilton Program for Schizophrenia Voices Questionnaire (HPSVQ) is a brief self-report measure which requires further psychometric evaluation. Methods: Using data from a transdiagnostic sample of 401 adult UK patients, the fit of a conceptual HPSVQ measurement model, proposing a separation between physical and emotional voice-hearing characteristics, was tested. A structural model was examined to test associations between voice-hearing, general emotional distress (depression, anxiety, stress) and wellbeing. The invariance of model parameters was examined across diagnosis and sex. Results: The final measurement model comprised two factors named ‘voice severity’ and ‘voice-related distress’. The former comprised mainly physical voice characteristics and the latter mainly distress and other negative impacts. Structural model results supported voice-related distress as mediating the associations between voice severity and emotional distress and wellbeing. Model parameters were invariant across psychosis versus non-psychosis diagnosis and partially invariant across sex; with females experiencing more severe and distressing voices and a more direct association between voice severity and general anxiety. Conclusions: The HPSVQ is a useful self-report measure of voice-hearing with some scope for further exploration and refinement. Voice-related distress appears a key mechanism by which voice severity predicts general distress and wellbeing. Whilst our data broadly support interventions targeting voice-related distress for all patients, females may benefit from learning to respond to voices in a less resistant mannerespecially from interventions targeting voice severity and strategies for responding