bluuebunny/crossref_metadata_2025_split huggingface dataset:
Proton transfer in small model systems: A density functional study
Authors: Barone Vincenzo , Orlandini Laura , Adamo Carlo 
Published: December 2004

AbstractThe structures, interaction energies, and proton‐transfer features of some representative intermolecular complexes are determined by using a density functional which incorporates gradient corrections and, as recently suggested by Becke, some Hartree–Fock exchange. The results are compared with those obtained by high‐order many‐body perturbation theory and by a number of more conventional density functionals. Hydrogen‐bond strengths and interatomic distances between heavy atoms are well reproduced by several density functionals. However, inclusion of some Hartree–Fock exchange is mandatory to improve XH bond lengths, and, especially, energy barriers governing proton transfer. Use of the new functional significantly improves the agreement with experimental and post‐Hartree–Fock results. This paves the route for a detailed theoretical study of proton‐transfer processes in large, biologically significant systems. © 1995 John Wiley & Sons, Inc.
Comparison of the performance of various gradient‐corrected exchange and correlation functionals in density functional theory: Case studies of CO and N2O molecules
Authors: Chermette H. , Lembarki A. , Gulbinat P. , Weber J. 
Published: December 2004

AbstractAn investigation of the influence of various gradient‐corrected exchange and correlation functionals on the bond lengths and dipole moments of CO and N2O has been carried out using density functional theory. It is shown that whereas some functionals are found to be more sensitive to the basis set quality than are others, the more commonly used gradient‐corrected functionals lead to properties in very good agreement with experiment provided that a sufficiently large basis set is employed. © 1995 John Wiley & Sons, Inc.
Applications of some bounds to density functionals for atoms
Authors: Porras I. , Gálvez F. J. 
Published: December 2004

AbstractIn this article, some applications of lower bounds to density‐dependent functionals in terms of radial expectation values are performed. These diverse applications include accurate upper bounds to the exact kinetic energy and to conjecture a wide set of relationships among radial and momentum expectation values. Some open questions for the improvement of these results are remarked upon. © 1995 John Wiley & Sons, Inc.
Density functional calculations of structures and ionization energies for heavy group V cluster anions
Authors: Kaschner R. , Saalmann U. , Seifert G. , Gausa M. 
Published: December 2004

AbstractThe structure and electronic structure of heavy‐group V cluster anions (Sb, Bi) are calculated with density functional methods within the local spin density approximation (LSDA). The influence of gradient corrections of the exchange and correlation energy is investigated. The calculated vertical and adiabatic ionization energies are in very good agreement with data from photoelectron spectroscopy (PES) for Sb, whereas the relatively large deviations for Bi can be reduced by the consideration of relativistic effects in a scalar‐relativistic manner. Concerning the structures, a strong similarity to the corresponding P clusters was found. In particular, the negatively charged pentamers are planar rings (with similarities to the aromatic [C5H5]− anion) with especially high ionization energies. © 1995 John Wiley & Sons, Inc.
On the electronic structure of transition‐metal oxide cations:DFTCalculations for VO+ and MoO+
Authors: Broclawik Ewa 
Published: December 2004

AbstractTwo transition‐metal oxide diatomic cations, VO+ and MoO+ are considered in this article. Ground‐ and excited‐state properties of the cations are derived from spin‐polarized DF calculations, including spectroscopic constants and metal–oxygen bonding features. A set of ionization potentials are calculated and, for vanadium oxide, compared with photoelectron spectroscopy data and a few available ab initio calculations. All calculated properties are close to experiment, the agreement being much better than for other traditional quantum chemical calculations. Present results together with our earlier findings for neutral molecules provide an excellent confirmation of the good performance of DFT in the case of transition‐metal systems. © 1995 John Wiley & Sons, Inc.
Full ab initio calculation of second‐order Raman spectra of semiconductors
Authors: Windl W. , Karch K. , Pavone P. , Schütt O. , Strauch D. 
Published: December 2004

AbstractWe present the first full ab initio calculation of second‐order Raman spectra in semiconductors based on density functional perturbation theory. The method is applied to the Γ spectra of the elemental semiconductors diamond, silicon, and germanium and reproduces the experimental data excellently. Using first‐principles phonons, we also calculated the corresponding overtone densities of states and Γ Raman spectra employing phenomenological polarizability coefficients. Finally, we analyze the results of the different approaches pointing out the relevance of a full first‐principles derivation. © 1995 John Wiley & Sons, Inc.
Ab initio calculation of structural, lattice dynamical, and thermal properties of cubic silicon carbide
Authors: Karch K. , Pavone P. , Windl W. , Strauch D. , Bechstedt F. 
Published: December 2004

AbstractWe present first‐principles calculations of the structural, lattice dynamical, and thermal properties as well as Raman results for cubic silicon carbide (3C SiC). The plane‐wave pseudopotential approach to density functional theory (DFT) in the local density approximation has been used to calculate the equilibrium properties of 3C SiC, i.e., the ground‐state energy, the band structure, the valence electron density, the lattice constant, the bulk modulus, its pressure derivative, and the ionicity factor of the chemical bonds. The linear‐response theory within DFT has been used to obtain the phonon frequencies, the eigenvectors, and the mean‐square atomic displacements. Furthermore, we calculated the mode Grueisen parameters, the internal‐strain parameter, the elastic constants, the Born effective charge, and the high‐frequency dielectric constant. The specific heat at constant volume and at constant pressure, the thermal expansion coefficient, the temperature dependence of the lattice constant, and that of the isothermal and adiabatic bulk modulus have been derived within the quasi‐harmonic approximation. Finally, the second‐order Raman spectrum of 3C SiC has been calculated using phenomenological polarizability coefficients and ab initio frequencies and eigenvectors. © 1995 John Wiley & Sons, Inc.
A model for the charge capacity of 1T–TiS2 intercalated with Li
Authors: Mendizabal Fernando , Contreras Renato , Aizman Arie 
Published: December 2004

AbstractThe variation of the charge capacity of a double‐layer 1T–TiS2 model system upon increasing intercalation with lithium is examined at a molecular level. The charge capacity is modeled through the global hardness index of density functional theory. The results obtained qualitatively reproduce the experimental trend observed in the voltage–composition variation curve in this system. Comparison with previous theoretical models show that the present approach may give a more complete information about the double‐layer capacitance, since it takes into account the lithium ionicity and the host–guest specific interactions. © 1995 John Wiley & Sons, Inc.
Nonlocal density functional calculations of the jellium metal surface
Authors: Jȩdrzejek C. , Wyżliński A. , Gryko J. 
Published: December 2004

AbstractThe Becke exchange functional is used for calculation of properties of the jellium model using the slab geometry inside a box with the infinite potential barriers at the boundaries. We simplify semianalytical representation of matrix elements. We calculate the surface energies and work functions with self‐consistent electron densities. For all densities (here, we give results in erg/cm2 for rs = 2.07 bohr, in comparison with the LSD approximation (−602)) and the uncorrected Pw GGA‐II (−730), the Becke‐II exchange only (−1212), and the Becke‐II exchange with Perdew86 correlation (−830) [always close to Pw GGA‐I (−814)] give smaller surface energies. The most important factor determining values of surface energies from different GGAS seems to be a form of a correlation potential. We also calculate the effect of finite slab thickness and the vacuum region thickness on the surface energy at the LSD level and indicate its importance in various jellium model calculations. © 1995 John Wiley & Sons, Inc.
Signal‐to‐noise measurement in X‐ray photoelectron spectroscopy
Authors: Koenig M. F. , Grant J. T. 
Published: December 2004

AbstractA study of signal‐to‐noise (S/N) was made in a Kratos ES300 XPS system on a variety of materials using both monochromatic and conventional X‐ray sources covering a wide range of count rates. Equations relating S/N to total counts (S + B), background (B), and the signal‐to‐background (S/B) ratio were derived and tested for data obtained in a system limited by noise from counting statistics.
Quantitative composition‐depth profiles of thin films
Authors: Frankenthal R. P. , Siconolfi D. J. 
Published: December 2004

AbstractA technique utilizing a layer by layer analysis has been developed for obtaining the composition‐depth profiles of thin films from Auger electron spectroscopy (AES) combined with ion sputtering. The technique, which has monolayer resolution and gives significantly more accurate results than prior methods, has been used for analyzing the composition of the native oxide on a series of iron‐chromium alloys. The new results differ significantly from those that do not consider layer by layer variations in composition, and they are in good agreement with those obtained some years ago by ion‐scattering spectrometry (ISS). In addition, it was confirmed that no preferential sputtering of Fe or Cr occurs during argon ion sputtering of the alloys.
Effect of hydroxylation upon the ion scattering spectra of oxide surfaces
Authors: Kelso J. F. , Pantano C. G. 
Published: December 2004

AbstractThe low energy sputter peak is an artifact found in many ISS spectra at energies below those predicted for binary elastic backscattering. In this study, a correlation is shown between the intensity of the low energy sputter peak in 3He+ ion scattering spectra and the degree of hydroxylation of the surfaces of silicon and aluminum oxide. The spectra for the clean and hydroxylated surfaces of silica glass (SiO2) were examined. It was found that as the degree of hydroxylation increased, the sputter peak intensity increased and the amount of elastic scattering from surface atoms decreased due to atomic shielding by the chemisorbed hydroxyls. The spectra for materials hydroxylated in bulk (silica gel (SiO2·nH2O) and gibbsite (Al(OH)3)) were also analyzed and these further verified this interpretation of the sputter peak intensity. On the basis of these observations, the low energy sputter peak in ISS has been attributed to the detection of positively sputtered ions such as the hydrogen (H+) and matrix species (e.g., Si+, SiO+, and O+). These were detected in a separate experiment by secondary ion mass spectroscopy (SIMS). It could not be determined whether the dependence of the sputter peak intensity upon the extent of hydroxylation is due solely to the sputter ion yield of hydrogen species or is related, in part, to an enhancement of the secondary ion yields of the oxide matrix species as well.
Effect of oxygen exposure on Auger spectra
Authors: Sherman Robert 
Published: December 2004

AbstractThe effect of residual vacuum contamination on Auger spectra, and subsequently on quantitative analysis, is well known. These effects become especially obvious when measuring the extent of phosphorus grain boundary segregation in the many alloys that require various methods of in situ fracture. To gain insight into the effects of vacuum contamination on the phosphorus Auger signal, we exposed a grain facet to controlled oxygen dosages and monitored the decreasing phosphorus‐to‐iron PPHR as a function of the increasing oxygen‐to‐iron PPHR. This communication reports the results of this experiment and suggests ways to compensate for vacuum contamination.
Primary‐beam diffraction modulated electron emission (PDMEE) for surface structural analysis
Authors: Valeri S. , Di Bona A. , Gazzadi G. C. 
Published: December 2004

AbstractScattering interference of primary exciting electrons leads to a dependence of the Auger emission intensity on the beam incidence angle. For beam energy in the kiloelectron‐volt range, maxima in the Auger yield occur when the primary beam is aligned with low‐index crystal axes, therefore the Auger angular intensity distribution directly reflects the symmetries and the degree of local order. We investigated the potential for this effect, primary‐beam diffraction modulated electron emission (PDMEE) to be used for surface structural characterization, in comparison with the Auger electron/photoelectron diffraction (AED/PD) technique. The angular intensity distributions of both low and high kinetic energy Auger electrons were measured on both GaAs and InP (110) surfaces. We show, by using highly collimated energetic electron beams, that the angular resolution is significantly improved in PDMEE with respect to AED/PD. Unlike the AED/PD case, the angular intensity distribution is independent of the kinetic energy of the Auger electrons, therefore low‐energy, surface‐sensitive electrons also directly reflect crystal symmetries, owing also to the fact that the specific momentum character of the Auger electrons can be neglected. Anisotropy in the intensity angular distribution as large as 70% was measured, comparable to AED/PD anisotropy values. Both a retarding field (low‐energy electron diffraction optics) and a dispersion field cylindrical mirror analyser were used for PDMEE analysis, and instrumental performances are discussed comparatively.
Secondary ion yields depending on the primary oxygen ion energy in cameca IMS‐4f instrument
Authors: Tomita M. , Homma Y. , Saito K. 
Published: December 2004

AbstractThe secondary ion yields of six element in silicon were measured as a function of the primary oxygen ion energy in a Cameca IMS‐4f SIMS instrument. The ion yields of elements with a high ionization potential decrease steeply with primary ion energy owing to the decreasing surface oxygen concentration. The decrease of the ion yield depends on the ionization potential. This relation and the known relative sensitivity factors enable a semiquantitative analysis of impurities in silicon to be carried out without standard samples.A similar study combined with oxygen flooding shows that the yields are now very high and independent of the primary ion energy. Profile distortions due to segregation effects, however, can occur.A comparison of the ion yields obtained with and without energy offset under low and high oxygen surface coverage shows that the shape of the arsenic secondary ion energy distribution is drastically changed leading to pronounced differences in ion yields.
Direct observation of a Pb–dithiophosphinate complex on galena mineral surfaces using SIMS
Authors: Brinen J. S. , Nagaraj D. R. 
Published: December 2004

AbstractStatic SIMS measurements of galena mineral surfaces after diisobutyl dithiophosphinate adsorption shows the presence of a 1:1 complex of the reagent and Pb. This assignment is based not only on the observed mass but on the observed isotope ratio.
Cytology and immunocytochemistry of the nucleus of the lateral line lobe in the electric fish Gnathonemus petersii (mormyridae): Evidence suggesting that GABAergic synapses mediate an inhibitory corollary discharge
Authors: Mugnaini Enrico , Maler Leonard 
Published: December 2004

AbstractKnollenorgans, Low‐threshold electoreceptors found in mormyrid fish, are involved primarily, if not exclusively, in communication. The rhombencephalic nucleus of the lateral line lobe (nLLL) is the target nucleus of knollenorgan afferents. Cells in the nLLL receive a few medium size to large endings with round synaptic vesicles (classified as spoon; large club; small club‐, and rodlet‐shaped endings) with which they form nexus (gap junction) and asymmetrical chemical synapses associated with the round synaptic vesicles. In addition these endings emit thin collaterals which terminate as small boutons on nLLL neurons; these boutons also have round vesicles and make mixed (electrotonic and chemical) synapse. In addition, cells in the nLLL receive synaptic input from numerous small boutons containing pleomorphic vesicles and making symmetric synapses. We have not found any interneurons within nLLL. Our ultrastructural analysis suggests that boutons synapsing on nLLL neurons belong to only two afferent fiber systems and that the wiring diagram of nLLL is extremely simple. We have studied the immunolocalization in nLLL of glutamic acid decarboxylase (GAD), the enzyme essential for the synthesis of GABA that is also a useful marker for this widely distributed inhibitory neurotransmitter. GAD immunoreactivity was confined to the small boutons with pleomorphic vesicles. GAD was also found in a nucleus projecting to the nLLL, here named the sublemniscal nucleus (SL), which probably conveys corollary discharge signals to the nLLL. This GABAergic projection may be responsible for the potent inhibition associated with the electric organ discharge command that has been described in these cells.
Contrasting properties of K+ conductances induced by baclofen and γ‐aminobutyric acid in slices of the guinea pig hippocampus
Authors: Ogata Nobukuni , Inoue Masumi , Matsuo Tadashi 
Published: December 2004

AbstractProperties of membrane K+ conductances induced by baclofen and γ‐aminobutyric acid (GABA) in the hippocampus were investigated by using guinea‐pig brain slices.Baclofen hyperpolarized the membrane and decreased the input resistance of pyramidal cells through the activation of a membrane K+ conductance.GABA caused a biphasic response in pyramidal cells, consisting of hyperpolarizing and depolarizing components. Combined application of picrotoxin and bicuculline eliminated the major part of the depolarizing component of the biphasic response and produced a relatively pure hyperpolarizing response which was also mediated by an increase in K+ conductance.The K+ conductance change induced by baclofen showed prominent inward rectification. However, the K+ conductance induced by GABA did not show an obvious rectifying property.The K+ conductance activated by baclofen was strongly antagonized by a low concentration (5 × 10−6 M) of 4‐aminopyridine (4‐AP). In contrast, the K+ conductance activated by GABA was insensitive to 4‐AP even at a high concentration of 10−3 M.The slow inhibitory postsynaptic potential (slow i.p.s.p.) evoked by stimulation of the mossy fibres was totally suppressed by a low concentration of baclofen (5 × 10−6 M). Whereas GABA (10−3 M) decreased the amplitude of the slow i.p.s.p., the reduction of the amplitude was proportional to the decrease in the amplitude of the electrotonic potentials produced by constant inward current injections.These results suggest that the hyperpolarizations induced by GABA and baclofen may be generated by K+ conductances of different kinetic and pharmacologic properties.
Serum protein leakage in aged human brain and inhibition of ligand binding at alpha2‐ adrenergic and cholinergic binding sites
Authors: Pappolla Miguel A. , Andorn Anne C. 
Published: December 2004

AbstractSerum proteins are known to extravasate into the brain parenchyma in senile and presenile dementia (Glenner: Hum. Pathol. 16:433–435, 1986; Wisniewski and Kozlowski: Ann. NY Acad. Sci. 396:119–129, 1982). We have recently demonstrated that human serum Cohn fraction IV (alpha‐globulin enriched) inhibits ligand binding at putative dopamine and serotonin2 receptors labeled by [3H]spiroperidol in human brain (Andorn, Pappolla, Fox, Klemens, and Martello: Proc. Natl. Acad. Sci. USA 83:4572–4575, 1986). We now demonstrate that serum proteins can be identified in the neuropil and in neuronal cell bodies in normal aged brain, that alpha‐globulin‐enriched fractions inhibit ligand binding at alpha2‐adrenergic and muscarinic binding sites in human brain as well, and that serum proteins can be identified within neuronal cytoplasm and axons.
The GABAA receptor: New insights from single‐channel recording
Authors: Mathers D. A. 
Published: December 2004

AbstractThe GABAA receptor of mammalian neurons exists as a macromolecular complex incorporating several interacting components. These include a chloride‐permeable ion channel and a recognition site for GABA. The binding of GABA molecules at the latter site triggers the transient opening of the chloride ion channel, resulting in a flow of charge which inhibits the generation of action potentials in the cell. The precise amount of charge passed during this event is modulated by ligand binding at at least three regulatory sites. These sites act as receptors for barbiturates, benzodiazepines, and certain convulsants. The extracellular patch clamp method has now been used to study the gating of chloride channels by GABA and the modulation of this process by drugs.Even in the absence of drugs, GABAA channels exhibit gating behavior, indicating the presence of multiple open and closed states and of substate conductance levels. GABAA channels from different preparations show considerable diversity in their detailed gating characteristics.In the presence of the barbiturate pentobarbital, GABAA channels open in prolonged bursts, consistent with the potentiating effect of this drug on macroscopic GABA responses. In contrast, the convulsant penicillin decreases charge transfer through open GABAA channels by shortening the average duration of the open state. Benzodiazepine receptor ligands exert complex effects on the GABAA channel. A general model of barbiturate and benzodiazepine potentiation of GABAA receptor responses is proposed.