The electronic structure of the boron hydrides

In parts I and II of this series [1] it has been demonstrated that localized three centre and two centre bonds may be used as basic functions for molecular orbital calculations on closed (cage) and open (basket) boron polyhedral molecules. In the present paper it is shown that the face and edge matrices of this theory are related to incidal and 1 and 2 simplexial matrices in the same way that Hückel matrices in the theory of unsaturated hydrocarbons are related to incidal matrices and 0 and 1 simplexial matrices. The theory is thus a topologically-correct extension of Hückel theory to three dimensions.

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Zusammenfassung In Teil I und II dieser Serie [1] wurde demonstriert, da\ lokalisierte Dreizentren- und Zweizentren-Bindungen als Basisfunktionen für MO-Rechnungen bei geschlossenen (KÄfig) und offenen (Korb) polyhedralen Borwasserstoff-Molekülen benutzt werden können. In der vorliegenden Arbeit wird gezeigt, da\ die OberflÄchen- und Randmatrizen dieser Theorie mit Incidal- sowie 1- und 2-Simplexmatrizen verwandt sind, in derselben Art wie die Hückel-Matrizen in der Theorie der ungesÄttigten Kohlenwasserstoffe mit Incidal-Matrizen sowie 0- und 1-Simplexmatrizen in Beziehung stehen. Die Theorie ist somit eine topologisch korrekte Erweiterung der Hückel-Theorie auf drei Dimensionen.

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Résumé Dans les parties I et II de cette suite d'articles on a démontré que des liaisons localisées à trois et à deux centres peuvent Être employées comme fonctions de base pour des calculs d'orbitales moléculaires sur des molécules polyhédriques boriques fermées («cage») et ouvertes («panier»). Dans cet article on montre que les matrices «faces» et «arÊtes» de cette théorie sont liées aux matrices d'incidence et aux matrices Simplexes 1 et 2 de la mÊme manière que dans la théorie de Hückel la matrice hamiltonienne est reliée aux matrices d'incidence et simplexes 0 et 1. La théorie est donc une extension à trois dimensions, correcte du point de vue topologique, de la méthode de Hückel.

     

A new approach for second‐order perturbation theory

A new second‐order perturbation theory (MP2) approach is presented for closed shell energy evaluations. The new algorithm has a significantly lower memory footprint, a lower FLOP (floating point operations) count, and a lower time to solution compared to previously implemented parallel MP2 methods in the GAMESS software package. Additionally, this algorithm features an adaptive approach for the disk/distributed memory storage of the MP2 amplitudes. The algorithm works well on a single workstation, small cluster, and large Cray cluster, and it allows one to perform large calculations with thousands of basis functions in a matter of hours on a single workstation. The same algorithm has been adapted for graphical processing unit (GPU) architecture. The performance of the new GPU algorithm is also discussed. © 2016 Wiley Periodicals, Inc.     

Microcapillary liquid chromatography/tandem mass spectrometry using alkaline pH mobile phases and positive ion detection

Extending the dynamic range of microcapillary liquid chromatography/tandem mass spectrometry (LC/MS/MS) peptide sequencing methods is essential for extracting new discoveries from proteomic studies. The complexity of global protein digests and in vivo processed peptide repertoires (as isolated from immunologically important HLA complexes) have led to the development of novel separation methods to increase the number of peptides identified by a single analysis. Separation of complex mixtures by multidimensional high-performance liquid chromatography (HPLC) decreases the number of isolated peptides contained in each fraction and increases the likelihood of detecting low abundant peptides in a background of dominant signals. In this study, we have evaluated the use of two dimensions of reversed-phase chromatography for resolving and sequencing naturally processed HLA-A2 presented peptide repertoires. The first dimension of separation was reversed-phase chromatography using the strong ion pairing reagent trifluoroacetic acid (TFA) to ensure the highest efficiency of peptide fractionation. The second dimension of reversed-phase chromatography was online with an electrospray ionization (ESI) ion trap mass spectrometer. Mobile phases used for the second dimension of chromatography were modified with volatile reagents including a contemporary acetate-modified acidic solvent, which was compared with mobile phases prepared with ammonium hydroxide at an alkaline pH. As expected, we demonstrate improved separation of the HLA-A2 presented fractions using the alkaline pH conditions. However, less obvious was the improved peptide signal-to-noise detected for peptide signals by positive ion ESI ion trap mass spectrometric detection, which was attributed to a reduced chemical background when using the alkaline pH mobile phases that allowed the ion trap to fill with the peptide ions until the automatic gain control detected a full trap. The term 'wrong-way-round ionization' has been used to describe intense [M+H](+) ions generated during ESI under strongly basic solutions. Ultimately, a larger number of the HLA-A2 peptide repertoire was sequenced by coupling TFA-modified reversed-phase fractionation with alkaline-modified microcapillary LC/MS/MS analysis of each fraction. In the present report, we compare the two second-dimension approaches and demonstrate the quality of data that was acquired using alkaline pH reversed-phase conditions.     

Thermodynamics of non-electrolyte transfer between octanol and water

The apparent enthalpy, free energy and entropy of transfer from aqueous buffer (pH 7) to water-saturated octanol were determined for the aliphatic alcohols methanol to octanol using an isoperibol flow-calorimeter. For the higher homologues, a linear relationship between enthalpy and free energy change is found indicating an enthalpy-entropy compensation effect. The thermodynamics of transfer were rationalized in terms of the thermodynamics of solvation in the separate phases, including water itself as a solute. The role of water as a cosolvent in the octanol phase is discussed.Presented at the sixth Italian meeting on Calorimetry and Thermal Analysis (AICAT) held in Naples, December 4–7, 1984.     

Nature of the stable oxide layer formed on an aluminum surface by work function measurements

The interaction of oxygen with clean aluminum results in formation of a stable oxide layer on the surface of the metal. This stable layer has a lower work function than that of clean aluminum. The nature of this stable layer is studied by measurement of work function changes. Heating of the stable layer, formed at room temperature and low oxygen pressures' (~10^?8 torr), in ultra-high vacuum resulted in a further decrease in the work function. The extent of this additional decrease was a function of temperature and the changes in work function caused by heating were irreversible in nature. At high oxygen pressures (p_O2 > 10^?2 torr) the effect of growth of incorporated oxide on the net limiting work function change appears to be small and the reversible changes in the work function are mainly a result of the variation in the amount of surface oxide. At 250°C, the contribution of incorporated oxide to net limiting work function change was dependent on oxygen pressure when it was formed at low oxygen pressures (P < 10^?7 torr). However, when the incorporated oxide was formed at oxygen pressures above 10^?7 torr, its contribution to the limiting work function change and, perhaps, the structure of the incorporated oxide itself were nearly independent of oxygen pressure. The difference in limiting work function change at various oxygen pressures was mainly because of the difference in the limiting amounts of surface oxide. Similar behavior is expected at room temperature.     

Thermoelastic investigations for fatigue life assessment

An investigation is presented on the suitability and accuracy of a thermoelastic technique for the analysis of fatigue cracks. The stress intensity factor ranges ΔK _I and ΔK _II are determined from thermoelastic data recorded from around the tip of a sharp slot in a steel specimen under biaxial load, in order to assess the accuracy of the technique. ΔK _I and ΔK _II are determined to within 4% and 9% of a theoretical prediction, respectively. The results from a similar test on a fatigue crack under biaxial load are also presented. These show that thermoelastic stress analysis is a rapid and accurate way of analyzing mixed-mode fatigue cracks. A discussion is given on the potential of thermoelastic stress analysis of propagating cracks.     

Near-edge Optical Properties of CuInSe2 Studied by Photoacoustic Spectroscopy

Optical absorption spectra of n-type CuInSe₂ single crystals were evaluated by means of photoacoustic spectroscopy in the photon energy range from 0.94 to 1.02 eV. At photon energies below 0.99 eV the spectra exhibit exponential tails that are ascribed to the presence of shallow impurity states. At higher photon energies the absorption coefficients follow the relation for direct allowed optical transitions between parabolic bands. The parameters of this relation are determined and compared with previous measurements.     

Optical Investigation of Defects in p-type CuInSe2 Single Crystals

Optical absorption spectra in the photon energy range from 0.03 to 1.1 eV and photoreflectance spectra in the range of the fundamental edge are measured on p-type CuInSe₂ single crystals. Besides a dominant contribution to the absorption coefficient due to intervalence band transitions below about 0.75 eV the spectra revealed five additional structures that can be ascribed to defect induced optical transitions with characteristic energies between 0.48 and 0.72 eV. Based on a comparison of the near-edge optical absorption and photoreflectance spectra a shallow defect (donor or acceptor) with an ionisation energy of about 46 meV was identified.