Quantum behaviour of hydrogen and muonium in vacancy-containing complexes in diamond

Most solid-state electronic structure calculations are based on quantum electrons and classical nuclei. These calculations either omit quantum zero-point motion and tunnelling, or estimate it in an extra step. Such quantum effects are especially significant for light nuclei, such as the proton or its analogue, μ+. We propose a simple approach to including such quantum behaviour, in a form readily integrated with standard electronic structure calculations. This approach is demonstrated for a number of vacancy-containing defect complexes in diamond. Our results suggest that for the NHV- complex, quantum motion of the proton between three equivalent potential energy minima is sufficiently rapid to time-average measurements at X-band frequencies

Linear polarization structures in LOFAR observations of the interstellar medium in the 3C 196 field

This study aims to characterize linear polarization structures in LOFAR observations of the interstellar medium (ISM) in the 3C196 field, one of the primary fields of the LOFAR-Epoch of Reionization key science project. We have used the high band antennas (HBA) of LOFAR to image this region and Rotation Measure (RM) synthesis to unravel the distribution of polarized structures in Faraday depth. The brightness temperature of the detected Galactic emission is 5−15 K in polarized intensity and covers the range from -3 to +8 rad m−2 in Faraday depth. The most interesting morphological feature is a strikingly straight filament at a Faraday depth of +0.5 rad m−2 running from north to south, right through the centre of the field and parallel to the Galactic plane. There is also an interesting system of linear depolarization canals conspicuous in an image showing the peaks of Faraday spectra. We used the Westerbork Synthesis Radio Telescope (WSRT) at 350 MHz to image the same region. For the first time, we see some common morphology in the RM cubes made at 150 and 350~{; ; \rm MHz}; ; . There is no indication of diffuse emission in total intensity in the interferometric data, in line with results at higher frequencies and previous LOFAR observations. Based on our results, we determined physical parameters of the ISM and proposed a simple model that may explain the observed distribution of the intervening magneto- ionic medium. The mean line-of-sight magnetic field component, B∥, is determined to be 0.3±0.1 μG and its spatial variation across the 3C196 field is 0.1 μG. The filamentary structure is probably an ionized filament in the ISM, located somewhere within the Local Bubble. This filamentary structure shows an excess in thermal electron density (neB∥>6.2 cm−3μG) compared to its surroundings

Environment of the Pbcenter at the Si(111)/oxide interface

10.1007/BF00203603Interface Science12139-146INSC

A theoretical study of desorption induced by electronic transitions in alkali halides

AbstractWe have studied desorption following the excitation of core- or valence-electrons using quantum chemical calculations of the potential energy surfaces. For core excitation, we simulate the state of two holes localised on a halogen ion using an extended semi-empirical molecular method (CNDO) to calculate the energy change associated with the displacement of the halogen ion or a neighbouring alkali ion. No instability was found for a bulk halogen ion with two localised holes, in agreement with recent experiments. However, also consistent with recent experiments, desorptive potential surfaces were obtained for both a (100) surface halogen ion with two localised holes and for a (100) surface alkali ion when two holes are localised on the nearest subsurface (second layer) halogen ion. We use the results of our earlier CNDO calculations to evaluate the energetics of desorption induced by valence-electron excitation and indicate the possible origin of atomic desorption. The difference between the experimental features of the desorption induced by core- and by valence-electron excitation are explained in terms of the differences in the energy surfaces and hence the coupling of the electronic excited states with the lattice

STUDY OF F CENTRES IN QUADRATIC AND ORTHOROMBIC CRYSTALS

Nous avons utilisé la méthode du réseau rigide ponctuel pour calculer la structure électronique des centres F dans BaClF, SrClF et BaCl2. Les positions relatives des bandes d'absorption des centres F en site F- ou Cl- ont été déterminées dans BaClF et SrClF. Dans BaCl2, les calculs de niveaux d'énergie suggèrent l'existence d'un seul type de centres F, ceux qui sont entourés par quatre ions Ba++.We present point-ion calculations of the electronic structure of F centres in BaClF, SrClF and BaCl2. The relative positions of the singlet and doublet absorption bands of the F centres at F- and Cl- sites have been determined in BaClF and SrClF. In BaCl2, calculations of energy levels suggest the existence of only the F centres which are surrounded with four Ba++ ions

The calculation of inter-atomic potentials using electron-gas models

3.00SIGLELD:9091.9F(AERE-R--10425). / BLDSC - British Library Document Supply CentreGBUnited Kingdo

A user's guide to MOLDY, a molecular dynamics program

3.00LD:9091.9F(AERE-R--8824) / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Corrosion studies on containment materials for vitrified high level nuclear waste Progress report for half-year ending 30 June 1983

LD:9091.9F(AERE-G--2856) / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo