A semiempirical MO study of the electronic structure and excited states of the Tris(2,2′-bipyridyl)Iron(II) and Tris(glyoxal-Bis-N-methylimine)iron(II)Ions

A semi-empirical SCF-MO method, the PEEL method, has been applied in an investigation of the electronic structure and excited states of two iron compounds, [Fe(II)-(GMI)₃]⁺⁺ and [Fe(II)-(bipy)₃]⁺⁺.The electronic absorption spectra have been recorded. The calculations show that it is necessary to account for the trigonal distortion and the covalency in order to explain these spectra quantitatively. Mössbauer measurements have also been performed. The calculated electronic population of the iron is in accord with Mössbauer isomer shift data, indicating that a realistic electron distribution has been obtained by the PEEL method.

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Zusammenfassung Eine semiempirische SCF-MO-Methode, die PEEL-Methode, wurde zur Untersuchung der Elektronenstruktur sowie von angeregten Zuständen der beiden Eisenverbindungen [Fe(II)-(GMI)₃]⁺⁺ und [Fe(II)-(bipy)₃]⁺⁺ angewendet.Die elektronischen Absorptionsspektren wurden aufgenommen. Die Berechnungen zeigen, daß die trigonale Verzerrung und die Kovalenz berücksichtigt werden müssen, um die Spektren quantitativ zu erklären. Mössbauer-Messungen wurden ebenfalls durchgeführt. Die berechnete Elektronenverteilung am Eisenatom ist in Übereinstimmung mit den Daten der Isomerenverschiebung der Mössbauer-Messungen, wodurch gezeigt wird, daß mit der PEEL-Methode eine realistische Elektronen-Verteilung erhalten wurde.

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Résumé Une méthode SCF-MO semi-empirique, la méthode PEEL, a été appliquée à une étude de la structure électronique et des états excités de deux composés ferreux: [Fe(II)-(bipy)₃]⁺⁺ et [Fe(II)-(GMI)₃]⁺⁺. Les spectres d'absorption électronique ont été enregistrés. Les calculs montrent qu'il est nécessaire de rendre compte de la distorsion trigonale et de la covalence pour expliquer ces spectres quantitativement.Des mesures de l'effet Mössbauer ont aussi été effectuées. La population électronique calculée du fer est en bon accord avec les données sur le déplacement isomérique de Mössbauer, ce qui indique que la méthode PEEL fournit une distribution électronique réaliste.

     

Khachiyan's linear programming algorithm

L. G. Khachiyan's polynomial time algorithm for determining whether a system of linear inequalities is satisfiable is presented together with a proof of its validity. The algorithm can be used to solve linear programs in polynomial time.     

Polarization contributions to the spin dependence of the effective interaction in neutron matter

We calculate the modification of the effective interaction of particles on the Fermi surface due to polarization contributions, with particular attention to spin-dependent forces. In addition to the standard spin-spin, tensor, and spin-orbit forces, spin nonconserving effective interactions are induced by screening in the particle-hole channels. Furthermore, a novel long-wavelength tensor force is generated. We compute the polarization contributions to second order in the low-momentum interaction V(low k) and find that the medium-induced spin-orbit interaction leads to a reduction of the 3P2 pairing gap for neutrons in the interior of neutron stars.     

Predictions of pulsed field gradient NMR echo-decays for molecules diffusing in various restrictive geometries. Simulations of diffusion propagators based on a finite element method

Pulsed field gradient NMR diffusometry is a promising tool for investigating structures of porous material through determinations of dynamic displacements of molecules in porous systems. A problem with this approach is the lack of closed analytical expressions for echo-decays in anything but idealized pore geometries. We present here an approach based on calculating the appropriate diffusion propagator by means of finite element calculations. The suggested method is quite general, and can be applied to arbitrary porous systems. The protocol for the calculations is outlined and we show results from some different cases: diffusion in confined geometries and in systems that are spatially inhomogeneous with respect to concentration.     

On the influence of the basis set superposition error on calculated vibrational frequencies

The relation between the so called basis set superposition error and intramolecular vibrational frequencies calculated at the Hartree Fock SCF level of approximation was investigated. A linear conformation of HF dimer was chosen as test system for the investigation. It was found that the direct basis set superposition error for the studied system is rather small. It was further found that the shifts are mainly determined by the geometry parameters of the system. AcknowledgementsJ. M. H.-R. wishes to thank the Ministerio de Educación, Cultura y Deporte for the award of a research grant.     

Locality properties of radial basis function expansion coefficients for equispaced interpolation

Natasha Flyer ^{Many types of radial basis functions (RBFs) are global in termsof having large magnitude across the entire domain. Yet, incontrast, e.g. with expansions in orthogonal polynomials, RBFexpansions exhibit a strong property of locality with regardto their coefficients. That is, changing a single data valuemainly affects the coefficients of the RBFs which are centredin the immediate vicinity of that data location. This localityfeature can be advantageous in the development of fast and well-conditionediterative RBF algorithms. With this motivation, we employ hereboth analytical and numerical techniques to derive the decayrates of the expansion coefficients for cardinal data, in both1D and 2D. Furthermore, we explore how these rates vary in theinteresting high-accuracy limit of increasingly flat RBFs.}     

Is analytical chemistry a self-generating science or depending upon problems and ideas from other scientific areas?

Summary Some aspects on the situation of analytical chemistry as science are presented. Two examples can illustrate the influence of other sciences on the progress of analytical chemistry.