bluuebunny/crossref_metadata_2025 huggingface dataset:
Near‐Hartree–Fock wave functions for solids: The case of crystalline silicon
Authors: Pisani C. , Dovesi R. , Orlando R.
Published: December 2004

Silicon is taken as a test system for assessing present‐day feasibility of calculations for crystalline solids of near‐Hartree–Fock quality. The calculations have been performed using CRYSTAL, an ab initio Hartree–Fock crystalline‐orbital LCAO program for periodic systems. The influence of the computational parameters that control the truncation of infinite sums on the results has been investigated; it is shown that a reasonable accuracy (numerical errors on total energy per atom below 10−3 a.u.) can be obtained while keeping the computational burden within manageable limits. The effect on the results of basis‐set size and quality is discussed. A number of basis sets have been tested, from minimal to relatively extended sets (28 atomic orbitals per atom). The quality of the wave function has been checked using variational criteria and also through a comparison with experimental data, such as equilibrium geometry, bulk modulus, electron charge density, and electron momentum distribution. For the latter quantities, which are a measure of the accuracy of the one‐electron density matrix, the best basis sets provide agreement with experiment that is almost within the experimental error. The correlation energy has been estimated using nonlocal density functionals, based on the one‐electron density matrix: After this correction, the atomization energy agrees with experiment to within 2%. The generalization of the above analysis to other crystals is briefly discussed.
Structural and electronic properties of infinite cis and trans polyenes: Perturbation theory of electron correlation effects
Authors: Suhai S.
Published: December 2004

The geometrical structure of five infinite polyene models (equidistant and alternating trans, equidistant cis, cis‐transoid, and trans‐cisoid) have been optimized using three different atomic basis sets at the Hartree–Fock level and by including electron correlation effects within the second order of Møller–Plesset perturbation theory. The single‐particle energy bands have also been corrected for correlation effects applying the electron polaron method. Bond alternation has always reduced the energy (both for trans and cis) polyenes but this stabilization energy has decreased with an increasing basis set and has saturated about 3 mH for trans and trans‐cisoid and about 7.5 mH for the cis‐transoid model. On the absolute energy scale, however, the alternating trans structure has always turned out to be more stable than either the cis‐transoid or the trans‐cisoid one. The energetic order is in all cases trans < cis‐transoid < trans‐cisoid. Using the largest basis set with correlation, the corresponding energy differences are ΔE(trans → cis‐transoid) = 1.69 mH and ΔE(trans → trans‐cisoid) = 6.12 mH, respectively. The HF values of the valence‐band widths vary in the region of 4–6 eV for the cis models and about 7 eV for the trans one. Correlation reduced them by about 20%, and the centers of the bands were shifted upward by about 2 eV due to self‐energy renormalization. The best values for the electron polaron valence bandwidths are 6.4, 4.2, 3.3, and 5.2 eV for the alternating trans, trans‐cisoid, cis‐transoid, and equidistant cis models, respectively. The vertical ionization potentials of the above four structures are 4.80, 5.47, 5.71, and 4.18 eV, respectively. The conduction bands have a width of 6–8 eV at the HF level (except equidistant cis with 4.6 eV for the larger basis sets) that will be reduced by about 15–20% due to polaron formation. The bands are shifted in this case uniformly downward by about 2–3 eV due to correlation. The best values obtained for the conduction bandwidths are 4.7, 6.4, 5.6, and 3.7 eV, respectively. These band shifts reduce the HF value of the fundamental gap by several eV's for all models. For the largest basis set, the ΔEgap values change from 6.6, 6.9, 7.7, and 5.3 eV (HF results for the alternating trans, trans‐cisoid, cis‐transoid, and equidistant cis models, respectively) to 2.7, 3.2, 4.5, and 2 eV, respectively, at the correlated level.
Molecular orbital cluster model study of bonding and vibrations of CO adsorbed on MgO surface
Authors: Pacchioni Gianfranco , Cogliandro Giuseppe , Bagus Paul S.
Published: December 2004

The interaction of CO with the MgO(100) surface has been investigated by means of all electron cluster model calculations. The CO molecule is bound on the Mg2+ site of MgO with a chemisorption energy of about 0.2 eV. The binding mechanism is electrostatic in nature and arises almost entirely from the interaction of the weak electric field generated by the ionic surface and the CO charge distribution, with negligible contributions from chemical effects as the CO σ donation. When CO is bound through carbon, its vibrational frequency increases with respect to the gas‐phase value. This shift, Δ, has been analyzed and decomposed into the sum of different contributions. It is found that the positive Δω does not arise entirely from the field–dipole interaction but is due, in part, to the increase in Pauli repulsion occurring when the CO molecule vibrates in the presence of the surface “wall.” A stronger electrostatic interaction, bringing the CO adsorbate closer to the surface, increases this wall effect and results in a more pronounced positive ω shift. It is also found that the two CO orientations exhibit opposite shifts in ωe, thus, the two orientations can be distinguished, in principle, by IR spectroscopy. The analysis of our ab initio cluster wave functions gives a very different picture than the standard view of the metal–CO bond as arising from σ donation and π back donation.
On the interaction of ions with a platinum metal surface
Authors: Seitz‐Beywl J. , Poxleitner M. , Probst M. M. , Heinzinger K.
Published: December 2004

Ab initio calculations have been performed to obtain analytical potential functions for describing the interactions between a platinum surface and both lithium and iodide ions. The accuracy of the results is tested by model calculations with large basis sets and the inclusion of correlation energy. The potentials obtained are to be used in computer simulations of electrochemical phenomena near solid–liquid interfaces.
Ab initio force field for simulations of proteins and nucleic acids
Authors: Aida Misako , Corongiu Giorgina , Clementi Enrico
Published: December 2004

We present a new self‐consistent set of ab initio analytical pair potential to predict specific nonbonded interactions of protein with nucleic acid, of protein with protein, and of nucleic acid with nucleic acid. The purpose of this study is to represent the interaction between biological molecules with an accuracy equivalent to the ab initio molecular orbital calculations, which are used as reference data to obtain the pair potentials. Atoms in nucleic acids and proteins are classified according to their chemical environments. An “effective charge,” a modification of a charge obtained from the Mulliken population analysis, is introduced and used to represent the electrostatic energy. More than 30,000 SCF interaction energies have been calculated to provide the reference data for the fitting procedure that we have adopted in the parameterization of the potentials. The standard deviation is 1.61 kcal/mol for interaction energies spanning the range from about −220 kcal/mol to +20 kcal/mol. Molecular dynamics simulations, using the above new set of force field, have been performed successfully for the systems where adequate treatments of specific interactions are required: The stability of α‐helix of C‐peptide and the interaction of spermine with oligonucleotide are examined as preliminary examples.
Calculation of 13C‐NMR chemical shift using the intermediate neglect of differential overlap model
Authors: Baker John David , Zerner Michael C.
Published: December 2004

The local origin/local orbital (LORG) method of Hansen and Bouman has been implemented with the intermediate neglect of differential overlap Hamiltonian for spectroscopy (INDO/S). The method is shown capable of demonstrating the inductive effects associated with electron‐withdrawing substituents through the diamagnetic shielding term. In addition, the method is capable of differentiating chemical shift in differing bond environments. The calculated paramagnetic contribution, however, is deficient for substituents that saturate the minimal basis such as oxygen and fluorine, which severely limits the general utility of the procedure. Through the utilization of reduced linear equations for the paramagnetic term, the method is amenable to any molecule for which a self‐consistent field can be performed and therefore can potentially be used to study very large systems. At present, however, the LORG method when used with the rapid INDO/S model Hamiltonian does not reliably reproduce the paramagnetic contribution to the shielding.
Molecular aspects of superconductivity: The role of the one‐particle term at the gap formation
Authors: Svrček Michal , Baňacký Pavol , Zajac Anton
Published: December 2004

An exact solution for the electron‐vibrational problem of the nonadiabatic molecular system has been obtained. By the quasi‐particle transformation technique, the fermionic Hamiltonian has been derived and solved at the ab initio level. Results clearly and unambiguously show that the gap formation due to nonadiabatic electron–phonon coupling is mediated by the one‐particle electron–phonon interaction term, whereas the two‐particle one represents just a correction to the correlation energy. The temperature dependence of the gap and electronic specific heat connected with the electron–phonon coupling have also been derived.
Novel pentacoordinated bridged silicon anions
Authors: Davis Larry P. , Burggraf Larry W. , Gordon Mark S.
Published: December 2004

Both ab initio and semiempirical electronic structure calculations are used to investigate the molecular and electronic structures and eneregetic stabilities of an unusual bridged compound with the general formula [YSiH3XSiH3Y]−, with Y = H or F and X = H, CH3, NH2, OH, F, or Cl. Most of these bridged anions are quite stable relative to YSiH3 + XSiH3Y−, and the stability is predicted to increase considerably when Y = H is replaced with Y = F.
To(Γ) phonons in GaAs under uniaxial strain
Authors: Lino A. T. , Meskini N. , Alves H. W. L. , Kunc K.
Published: December 2004

Using the density‐functional theory in the local‐density approximation, norm‐conserving pseudopotentials, and plane‐wave expansions, we have developed a simple way to calculate ab initio the uniaxial strain dependence of the TO(Γ) phonon mode in GaAs, including the envolved relaxations effects. The relaxation response of the system was evaluated from the use of the elasticity theory. Our results confirm the experimental evidence and show a reasonable agreement with the observed data for the frequency splitting of this phonon mode. © 1993 John Wiley & Sons, Inc.
Variational principle for transition matrix
Authors: Titov A. V.
Published: December 2004

A variational principle for the transition matrix is considered. Conception of the MC SCF (in particular, CASSCF) approach for the transition matrix is proposed as a solution of the variational problem on the optimal evolution of a packet of two stationary states with some additional conditions. An ordinary MC SCF method for a single state is a special case of the proposed approach. Some aspects of the solving of the equations for the optimal transition matrix are treated. The method can be used in atomic and molecular calculations of transition energies, oscillator strengths, and other properties. © 1993 John Wiley & Sons, Inc.
Closure property for free electrons
Authors: Brzeska D. , Olszewski S.
Published: December 2004

Some operators considered conventionally as Hermitian are not strictly Hermitian for the freeelectron states known especially in the case of solids. The consequences of this fact on the closure property are examined. © 1993 John Wiley & Sons, Inc.
Application of the GCA to a series of curve crossing topologies
Authors: Broeckhove J. , Keutgens W. , Lathouwers L. , Van Leuven P.
Published: December 2004

The generator coordinate approximation (GCA) for the calculation of spectra of diatomics is briefly reviewed. Results of this method applied to a series of curve crossings are presented. In all cases, the generator coordinate method performs significantly better than does the adiabatic approximation. When the energy gap becomes smaller, the GCA results improve. In the crossing limit, the GCA becomes exact. © 1994 John Wiley & Sons, Inc.
Theoretical study of the conjugation length effect on the electronic and second‐order nonlinear optical properties of amino–nitro diphenylacetylenes
Authors: Dehu C. , Brédas J. L.
Published: December 2004

We presnet a theoretical study of the effect of the conjugation length on the electronic properties and second‐order molecular polarizabilities β in p‐amino‐p′‐nitrodiphenylacetylene molecules where the number of triple bonds in the conjugated segment varies from 1 to 4. The β values are calculated via an intermediate neglect of differential overlap/single configuration interaction (INDO/SCI) sum‐over‐states (SOS) approach. We test the convergence of the SOS method and the validity of the two‐state model to describe the β response. The results indicate that increasing the conjugation length results in a decrease of the charge transfer within the molecule. The two‐state model is shown to break down as the conjugated segment extends to four triple bonds; this is due to the appearance of several low‐lying nearly isoenergetic excited states that significantly contribute to the β response. The theoretical results are in excellent agreement with recent experimental data. © 1994 John Wiley & Sons, Inc.
Practical expressions for the two‐center multipole expansion of r
Authors: Panas Itai
Published: December 2004

An explicit and transparent deduction of a conventional expression for the two‐center multipole expansion of the Coulomb potential, r, in terms of spherical harmonics, is perfomed. An intermediate expression in the deduction is shown to be well suited for transformation into a Cartesian representation. Practical formulas are produced that allow for safe and efficient implementations in computer programs. Electrostatic interactions between two pairs of point charges are computed and the importance to include the higher multipole interactions is stressed. © 1995 John Wiley & Sons, Inc.
Kinetics of atom–photon Interactions
Authors: Oláh K. , Bódiss J.
Published: December 2004

In order to avoid the violation of basic principles of macroscopic reversibility and detailed balance, we propose a cell kinetic model for atom‐photon interactions instead of Enstein's classical photon kinetic mechanism. Our model can be interpreted as a generalization of either mass action law or Einstein's original scheme. © 1995 John Wiley & Sons, Inc.
Isomeric interconversions in tamoxifen and related compounds: An AM1 study
Authors: Brewster Marcus E. , Huang Ming‐Ju , Pop Emil , Bodor Nicholas
Published: December 2004

Semiempirical molecular orbital techniques (AM1) were applied to the study of cis–trans isomerism in tamoxifen and related compounds. AM1‐derived structures were in good agreement with X‐ray data. Theoretical evaluation indicated that both cis‐ and trans‐tamoxifen as well as the 4‐hydroxytamoxifen isomeric pair were very close in energy, confirming experimental results suggesting nearly equivalent populations of the two isomers under equilibrium conditions. Mechanistic studies included a determination of selected proton affinities to establish the nature and location of compound protonation as well as conformational studies of the formed carbocations. In particular, internal rotation about the incipient olefinic CC bond in the tamoxifen and 4‐hydroxytamoxifen carbocations provided a likely reaction mechanism. There evaluations suggested that the more rapid isomerization of 4‐hydroxytamoxifen as compared to tamoxifen was related to transition‐state stabilization through phenolic oxygen electron donation. © 1995 John Wiley & Sons, Inc.
Coupled‐Cluster approaches with an approximate account of triply and quadruply excited clusters: Implementation of the orthogonally spin‐adapted CCD + ST(CCD), CCSD + T(CCSD), and ACPQ + ST(ACPQ) formalisms
Authors: Piecuch Piotr , Toboła Robert , Paldus Josef
Published: December 2004

The orthogonally spin‐adapted (OSA) coupled‐pair (CCD) methods with an approximate account of triply and quadruply excited clusters are considered. We focus on the CCD + ST(CCD) perturbative estimate of the singly and triply excited clusters due to Raghavachari [J. Chem. Phys. 82, 4607 (1985)] and its ACPQ + ST(ACPQ) analog proposed by Paldus and Piecuch [Int. J. Quantum Chem. 42, 135 (1992)]. The latter approach combines the perturbative treatment of singles and triples with an approximate CCD theory corrected for connected quadruply excited clusters (ACPQ). We also consider the OSA version of the CCSD + T(CCSD) method (coupled‐cluster [CC] approach with singly and doubly excited clusters and noniterative perturbative account of triply excited clusters) introduced by Urban et al. {J. Chem. Phys. 83, 4041 (1985)}. The explicit OSA expressions for the previously neglected {P. Piecuch and J. Paldus, Theor. Chim. Acta 78, 65 (1990)} S(CCD) and S(ACPQ) terms are derived using diagrammatic methods of many‐body perturbation theory and graphical methods of spin algebras. The CCD + ST(CCD), CCSD + T(CCSD), and ACPQ + ST(ACPQ) formalisms have been implemented and the general purpose ab initio programs have been written using a newly developed procedure for improving the convergence of the reduced linear equation method {P. Piecuch and L. Adamowicz, J. Chem. Phys. 100, 5857 (1994)}. Results of the pilot calculations for few nondegenerate and quasi‐degenerate systems are presented and compared with the full configuration interaction data. © 1995 John Wiley & Sons, Inc.
A microscopic coupled‐cluster treatment of electronic correlations in Hubbard models
Authors: Bishop R. F. , Xian Y. , Zeng C.
Published: December 2004

We recently applied the coupled‐cluster method (CCM) with considerable success to several novel quantum spin‐lattice systems in the infinite bulk limit. In this article, we extend our CCM analysis to the electronic Hubbard models. In particular, based on a systematic approximation scheme within the CCM, we investigate the zero‐temperature properties of Hubbard models at half‐filling and with a single hole on a general bipartite lattice. Our aim was to provide the CCM framework for a systematic calculation of the properties of Hubbard models. © 1995 John Wiley & Sons, Inc.
Spin‐Adapted restricted Hartree–Fock reference coupled‐cluster theory for open‐shell systems: Noniterative triples for noncanonical orbitals
Authors: Neogrády Pavel , Urban Miroslav
Published: December 2004

The coupled clusters singles and doubles (CCSD) method for calculations of open‐shell systems with the single restricted Hartree–Fock (ROHF) reference determinant is extended by the noniterative triples to give CCSD(T). Our approach profits from the fact that (a) single‐ and double‐excitation amplitudes are spin‐adapted, which directly leads to a computationally less demanding algorithm than are nonadapted procedures and produces the spin‐adapted CCSD wave function and (b) triple excitations calculated from converged spin‐adapted (SA) CCSD amplitudes are also obtained more effectively. Altogether, computer demands of our SA CCSD(T) approach, applicable to high‐spin open‐shell cases which are well represented by a single‐determinant reference is comparable to that for closed‐shell systems. Our approach is not based on semicanonical orbitals, applied by Bartlett's group. However, we compare some other possible choices of ROHF orbitals to this “standard.” Numerical results for a series of atoms and molecules demonstrate little sensitivity to this selection. © 1995 John Wiley & Sons, Inc.
Ab initio conformational study of the CO ⃛H2 van der Waals dimer
Authors: Salazar Mary C. , De Castro Alexandra , Paz José L. , Diercksen Geerd H. F. , Hernández Antonio J.
Published: December 2004

Quantum chemical fully ab initio conformational calculations were performed for the weakly bound van der Waals CO ⃛H2 dimer in the framework of the supermolecule approach. The counterpoise‐corrected interaction energies, computed through fourth‐order MBPT using the basis sets described recently by Sadlej, were in excellent agreement with results obtained with larger basis sets constructed to give accurate values for the electric moments and polarizabilities of CO and H2. The relative stability of the configurations studied here was collinear structures > parallel structure > T‐shaped structures. The collinear and parallel structures represent the most stable group of configurations. The present calculations show that they have values of De between 5.89 and 10.66 meV. The T‐shaped structures represent relatively less stable configurations with values of De between 0.84 and 2.92 meV. © 1995 John Wiley & Sons, Inc.
Application of the valence‐universal coupled‐cluster method based on various model spaces to 1S states of Be
Authors: Jankowski K. , Malinowski P.
Published: December 2004

The recently formulated atomically oriented valence‐universal theory (VU–CCSD/R) based on various complete model spaces is applied to the accurate description of the 2s2 1S, 2s3s 1S, 2p2 1S, and 3s2 1S states of Be. Two extensive 9s9p7d7f5g STO basis sets that differ by one s‐type function are employed. Both standard and nonstandard solutions of the VU–CC equations are considered. The eight values of the ground‐state energies obtained when considering various model spaces and basis sets were found to differ very little. The energies of the individual excited states disclosed a relatively weak dependence on the choice of model spaces defining the method (or, equivalently, on the fact whether they correspond to standard or nonstandard solutions). In turn, the energies of the excited states strongly depend on the STO basis set used in the calculations. To obtain a reliable description of both the ground state and excited states, well‐balanced STO basis sets have to be employed. © 1995 John Wiley & Sons, Inc.
Note on the variation step in the iteration–variation approach: Illustration on the hydrogen atom
Authors: Delhalle J. , Cizek J.
Published: December 2004

An analysis of the analytical properties of the first iterate of the iteration–variation approach applied to small Gaussian expansions is reported in the case of the hydrogen atom. The first iterates embody important qualitative improvements such as a cusp near the origin and better asymptotic decay at large values of r. Actual values of the properties depend on the quality of the initial functions in such a way that for very small Gaussian expansions the variation step is necessary. © 1995 John Wiley & Sons, Inc.
Spin‐unrestricted character of Kohn‐Sham orbitals for open‐shell systems
Authors: Pople John A. , Gill Peter M. W. , Handy Nicholas C.
Published: December 2004

It is argued that Kohn‐Sham calculations on open‐shell systems should be spin unrestricted in character. An application to the proton hyperfine constant in the methyl radical is presented. © 1995 John Wiley & Sons, Inc.
Nonlocal functionals for exchange and correlation in density functional theory: Application to atoms and to small atomic clusters
Authors: Alonso J. A. , Balbás L. C. , Rubio A.
Published: December 2004

The local density approximation (LDA) to exchange and correlation effects has well‐known limitations. The nonlocal weighted density approximation (WDA) corrects some of those defects. This is illustrated here by applications to free atoms and small atomic clusters. The WDA also induces a nonlocal kinetic energy functional that is tested for atoms. © 1995 John Wiley & Sons, Inc.
Frequency‐dependent linear response of superconducting systems
Authors: Lüders Martin , Gross E. K. U.
Published: December 2004

We present a density functional scheme for calculating the frequency‐dependent linear response of superconductors. The central result is a set of integral equations determining the linear response of the normal and anomalous densities to external perturbations. Analytic solutions of these integral equations are obtained for homogeneous systems with separable effective interactions. For inhomogeneous superconductors, the formalism leads to a scheme for calculating the critical temperature without explicitly solving the gap equation. © 1995 John Wiley & Sons, Inc.
Vibrational frequencies of sodium clusters
Authors: Aguilar J. G. , Mañanes A. , López M. J. , Iñiguez M. P. , Alonso J. A.
Published: December 2004

The vibrational frequencies of NaN clusters (2 ⩽ N ⩽ 72) are calculated by direct diagonalization of the dynamical matrix. Density functional theory with a spherically averaged pseudopotential is used to compute the total energy. The geometry is optimized by the simulated annealing technique. Contributions to the Hessian matrix due to electron relaxation following the ionic displacements are calculated in linear response theory. The frequencies are in the range 0‐220 cm−1 and the electron relaxation strongly modifies those of the modes dominated by radial oscillations, particularly the breathing mode frequencies that are proportional to N−1/3. The filling of atomic shells produces a stepwise behavior of the highest frequencies. The giant dipole resonance energies are obtained as a byproduct of the calculation. © 1995 John Wiley & Sons, Inc.
The Weizsäcker functional: Some rigorous results
Authors: Romera E. , Dehesa J. S. , Yañez R. J.
Published: December 2004

The Weizsäcker functional TW is a necessary element to explain basic physical and chemical phenomena of atomic and molecular systems in the general density functional theory initiated by Hohenberg and Kohn. Here, rigorous inequalities which involve the functional TW and two arbitrary power‐type density functionals ωα ≔ ∫ ρα(r)dr are found by the successive applications of Sobolev and Hölder inequalities. Particular cases of these inequalities give lower bounds to the Weizsacker functional of an N‐electron system in terms of a fundamental and/or experimentally measurable quantity such as, e.g., the Thomas–Fermi kinetic energy T0, the Dirac–Slater exchange energy K0 and the average electronic density 〈ρ〉 in doing so, some known relationships appear. A numerical Hartree–Fock study of the accuracy of some resulting lower bounds is carried out. Finally, rigorous relationships between the Weizsäcker functional and the Boltzmann–Shannon information entropy of the system under consideration are given. © 1995 John Wiley & Sons, Inc.
The quantitative analysis of surfaces by XPS: A review
Authors: Seah M. P.
Published: December 2004

A general framework is presented for the quantitative analysis of surfaces by X‐ray photoelectron spectroscopy (XPS or ESCA). The approach starts by considering analysis using reference data recorded on the same instrument and under identical conditions as the analysed sample. Matrix factors are evaluated and the quantification for adsorbed layers and sputter profiles discussed. More popularly reference data are not recorded each time but are taken from the published literature. In this case the angular anisotropy term and analyser transmission functions need to be known. These are discussed and the analyser transfer functions of commercial spectrometers are presented in detail. Nine published reference data sets are assessed to test their correlation with the theoretical predictions. Theree sets are found to give moderate agreement but agree more closely with each other in their divergence from the theory for particular elements. This divergence enables a peak intensity factor to be defined which quantifies the intensity lost from a peak due to shake‐up events, etc. With this factor and the analyser transfer functions quantification can be made to an accuracy of 10% in all instruments from a single reference data set.
Limitations of ion etching for interface analysis
Authors: Holloway P. H. , Bhattacharya R. S.
Published: December 2004

The limitations of using ion sputtering for interfacial analysis are reviewed. It is concluded that many artifacts may degrade interfacial resolution—surface roughness, zone of mixing, bulk and surface diffusion, implantation, residual gas adsorption and matrix effects. Techniques to minimize these limitations are suggested. Some examples are: use of reactive ion beams, multiple ion beams, sample rotation and special mounting, varying the ion energy and incidence angle, and deconvolution. It is concluded, however, that sputtering may destroy atomic arrangement and chemical state information at the interface, and new approaches are needed to determine these interfacial parameters.
Surface analysis by glow discharge
Authors: Berneron R. , Charbonnier J. C.
Published: December 2004

This paper deals with the possibilities of glow discharge spectroscopy for surface analysis of metals. After a brief résumé of the principles and characteristics of the technique, examples of results obtained are given concerning the control of sub‐surface compositions after thermal or thermometric treatment of steels; surface analysis of low carbon steel strip at various stages of the production process; analysis of phosphate surface coatings; control of the surfaces of specimens for laboratory experiments; and laboratory studies of passivation phenomena.
X‐ray photoelectron spectroscopy studies of fired palladium electrode ink materials
Authors: Brown N. M. D. , Hewitt J. A. , Meenan B. J.
Published: December 2004

The oxidation state of palladium in an electrode ink dispersion, air‐dried on barium titanate dielectric substrates, has been studied using x‐ray photoelectron spectroscopy (XPS) as a function of both firing temperature and firing atmosphere. Several different states have been identified in amounts which vary over the firing temperature range of interest, i.e. palladium metal, a so‐called PdOads species, PdO and palladium in one or more higher oxidation states. No significant differences were observed for the two different contacting atmospheres used during firing, namely air and flowing nitrogen. Owing to overlap of the Pd 3p3/2 and the O 1s spectral envelopes, peak fitting of the oxygen signal was not attempted. Small amounts of residual carbonaceous ash were detected for all the samples studied over the whole range of firing temperatures employed.

XPS analysis of a sample of the palladium ink, fired to 1350°C in air and subsequently etched using a fast atom bombardment (FAB) argon source, showed that the sub‐surface palladium was metallic in nature although the original metal surface was composed almost entirely of PdO. Thus, for these palladium inks, when fired to temperatures comparable with those used in multilayer ceramic capacitor (MLCC) manufacture, apart from a thin surface oxide layer the palladium present is in the metallic form, as required for electrode layer conduction.
Surface characterization of EVA copolymers and blends using XPS and ToF‐SIMS
Authors: Galuska A. A.
Published: December 2004

The surface chemistries of semi‐crystalline copolymers of ethylene (CH2CH2) and vinyl acetate (CH2CHCO2CH3) (EVAs) and blends of these copolymers with low‐density polyethylene (LDPE) have been examined critically for the first time using angle‐resolved XPS and time‐of‐flight SIMS (ToF‐SIMS) analyses. Specimens were fabricated using a variety of methods (commercial extrusion, spin coating and thermal compression) to determine the influence of processing conditions on EVA surface chemistry. The XPS and ToF‐SIMS analysis of these specimens has provided techniques for identifying surface EVA (also thermal oxidation), has provided both XPS and ToF‐SIMS methods for quantitative EVA analysis and has revealed the details of EVA surface chemistry. The XPS core‐level spectra indicate the presence of the ester (VA) and ether (surface oxidation) species, but do not provide positive EVA identification. The ToF‐SIMS spectra show features specific to both the ethylene and vinyl acetate portions of the polymer. Both XPS and ToF‐SIMS analyses have been calibrated to provide quantitative VA (error < 2 wt.% VA) and oxygen (error < 1.0 at.% oxygen) analyses. Surface VA content was found to increase linearly with bulk VA content, and was not influenced by the type of fabrication method used. The EVA surfaces appear to consist of two layers. The near‐surface region (> 20 Å depth) is dominated by a VA‐poor (ethylene‐rich) layer. This region is covered by a thin (⩽20 Å thick) VA‐enriched layer.
Spectroscopic characterization of stainless‐steel surfaces treated by plasma
Authors: Deshayes L. , Charbonnier M. , Prakash N. S. , Gaillard F. , Romand M.
Published: December 2004

Stainless‐steel substrates were surface treated then coated with thin amorphous hydrogenated carbon films that were deposited by CH4 plasma polymerization. The effects of these surface treatments were studied by x‐ray photoelectron spectrometry, ion scattering spectrometry and Fourier transform infrared spectrometry. A few minutes of O2 plasma treatment at a power density of 0.5 W cm−2 was shown to modify strongly the surface composition of these substrates, with chromium present at the surface being transformed gradually, from Cr2O3 to CrO3, before disappearing altogether. In contrast, NH3 plasma of similar power, but generated over a few seconds, cleaned and functionalized the surface. Both of these treatments proved to be highly efficient in promoting good carbon film adhesion to the substrate.
Effects of compounding and extrusion variables on degree of fusion and impact strength of PVC window profile
Authors: Batiste J. , Choi P. , Lynch M. , Rudin A. , De Carvalho L. H.
Published: December 2004

The effects of temperature in twin screw extrusion of a window profile compound have been studied. Compounds were made with and without an acrylic impact modifier. Fusion levels of the extruded profiles were rated from values of the rubbery plateau modulus at temperatures near 110°C. Impact strength was measured at room temperature using notched tensile specimens at 1 m/s jaw separation rate. The impact strength of these materials does not increase with fusion level once an adequate degree of gelation has been achieved. The impact‐modified compound shows a dramatic improvement in impact strength when the melt temperature was increased from 319°F to 343°F. A further increase to 365°F had no effect. The compound without impact modifier exhibited no improvements in impact strength over the whole extrusion temperature range. Conflicting reports in the literature on effects of fusion level on impact strength of PVC articles probably reflect different interactions between extrusion conditions and compound composition.
Über Komplexverbindungen. VII. Lichtabsorption von Mono‐ und Diacido‐amminen des dreiwertigen Kobalts mit Fettsäureresten
Authors: Linhard Martin , Weigel Melitta
Published: December 2004

Die Lichtabsorption von 38 Kobalt(III)amminkomplexen mit einem bzw. zwei in cis‐ oder trans‐Stellung koordinativ gebundenen Fettsäureresten wird im Gebiet von 15000 bis 45000 cm−1 gemessen und diskutiert.

Die Spektren bestehen im allgemeinen aus zwei niederen Banden I und II (log ϵ ∼ 2) im Sichtbaren und nahen U. V. und einer hohen Bande III (log ϵ ∼ 4) im entfernteren U. V.

Die Banden I und II gehören zu Elektronenübergängen in der Edelgaszwischenschale. Innerhalb der homologen Reihen der drei Salztypen weisen nur die Salze der stärkeren Säuren Abweichungen auf, die zwar deutlich und systematisch, aber gering sind. Allgemein liegen die Banden I und II gegenüber jenen der entsprechenden Luteosalze bei kleineren Wellenzahlen und zwar zunehmend in der Reihenfolge: Luteo → Acido → cis‐Diacido → trans‐Diacido‐komplexe. Die Bande I der trans‐Diacido‐komplexe spaltet hierbei deutlich in zwei Teilbanden auf. Für die übrigen niederen Banden wird eine (geringere) Aufspaltung der Bande I als wahrscheinlich, der Bande II als möglich befunden. Die Aufspaltung wird in Analogie zu Normalkomplexen als Folge der größeren oder kleineren Asymmetrie der Kraftwirkungen der Liganden gedeutet.

Aus der Bandenverschiebung und ‐aufspaltung ergibt sich eine brauchbare Regel für die Zuordnung von Diacido‐salzen zur ces‐ bzw. trans‐Reihe.

Die hohe U. V.‐Bande III ist dem Chromophor der Carboxylgruppe zuzuordnen, dessen Absorption durch die Komplexbindung stark nach kleineren Wellenzahlen verschoben ist, und zwar auf Grund ihrer gleichen Lage in Ammin‐ und Aethylendiaminkomplexen, ihrer starken Abhängigkeit von der Art der Fettsäureliganden, ihrer Beziehungen zu den Banden der freien Fettsäuren und zu den Bildungswärmen analoger stereoisomerer Salze.

Die viel weiter im U. V. zu erwartenden Amminbanden tauchen vollständig unter den Carboxylbanden unter.
Über die Reaktion von Borsäuremethylester mit Ammoniak und Aminen. II
Authors: Goubeau J. , Ekhoff E.
Published: December 2004

Es wird die Reaktion des Borester‐Ammoniakates H3N · B(OCH3)3 mit überschüssigem Borester studiert. Sie verläuft prinzipiell nach:\documentclass{article}\pagestyle{empty}\begin{document}$ \left({{\rm RO}} \right)_3 {\rm BNH}_3 \, + \,{\rm B}\,\left({{\rm OR}} \right)_3 \,\rightleftharpoons\,\left({{\rm RO}} \right)_3 {\rm B}\,\, \cdot \,\,{\rm NH}_2 {\rm B}\left({{\rm OR}} \right)_2 \, + \,{\rm CH}_3 {\rm OH} $\end{document} wird jedoch durch Folgereaktionen des primären Reaktionsproduktes infolge seines koordinativ ungesättigten Charakters mit dem Ausgangsmaterial, mit dem Lösungsmittel u. a. sehr kompliziert, so daß sehr mannigfaltige Reaktionsprodukte erhalten wurden. Bei extremer Entfernung aller flüchtigen Bestandteile hinterblieb das gesuchte Reaktionsprodukt, allerdings mit schlechter Ausbeute.
Umsetzung von Silicium mit Kupfer(I)‐chlorid. II
Authors: Kohlschütter H. W. , Klump O.
Published: December 2004

Die chemische Analyse der flüchtigen Reaktionsprodukte, die bei der exothermen Reaktion Si + 4 CuCl → SiCl4 + 4 Cu entstehen, hatte ergeben, daß sich neben dem Hauptprodukt SiCl4 als Nebenprodukte höhermolekulare Siliciumchloride mit (SiSi)‐Bindungen bilden und daß der Gesamtverlauf der Umsetzung autokatalytischen Charakter hat. Aus der thermischen Analyse des Reaktionsverlaufs war abgeleitet worden, daß die Reaktion mit einer Passivierung der Komponente Si beginnt. Als Überleitung von der Mitteilung I (die nur eine Übersicht über die Ergebnisse enthielt) wird in dieser Mitteilung II die Auswertung der thermischen Analyse ausführlich beschrieben. Anschließend wird gezeigt, daß die Befunde am System Si/CuCl in naher Beziehung stehen zu Erfahrungen über die Chlorierung von Silicium und über den Abbau höhermolekularer Siliciumchloride durch Cu bzw. CuCl, die bisher unabhängig von dem System Si/CuCl gewonnen wurden. Es werden experimentell gesicherte Teilreaktionen zusammengestellt, die auch beim Aufheizen des Systems Si/CuCl in der Grenzflächenzone der Komponente Si möglich sind. Diese liefern als Modellreaktionen Beiträge zum Verständnis des Reaktionsverlaufs bis zum sogenannten Sprungpunkt des Systems Si/CuCl.
Über die Darstellung und einige Eigenschaften des Bis(monofluorcarbonyl)peroxids ((FCO)2O2)
Authors: Arví A. J. , Aymonino P. J. , Schumacher H. J.
Published: December 2004

Es wird eine Methode beschrieben, mit deren Hilfe man aus Fluor, Kohlenmonoxid und Sauerstoff im Überschuß, das Bis(monofluorcarbonyl)peroxid (BMCP) präparativ herstellen kann. BMCP ist eine wasserklare Flüssigkeit, die bei tiefer Temperatur zu weißen Kristallen erstarrt. Smp. = ‐−42,5°C. Der Siedepunkt des BMCP liegt bei + 15,9°C. Die TROUTON‐Konstante beträgt 24,5 kcal/Mol °K. BMCP hat eine charakteristische Absorption im UR. Seine Absorption im UV ist kontinuierlich und beginnt bei 2660 Ä.

BMCP vermag die Polymerisation von Äthylenverbindungen auszulösen. Es zerfällt bei Temperaturen oberhalb von 200 °C explosionsartig. Die Druckerhöhung nach Reaktionsende beträgt 150%: (FCO)2O2 → F2CO + CO2 + 1/2 O2. Der explosive Zerfall in Gegenwart von überschüssigem CO führt zu einer 100proz. Druckerhöhung: (FCO)2O2 + CO → F2CO + 2 CO2.

Der langsame Zerfall des BMCP ergibt Druckerhöhungen zwischen 100% und 150%. Bei diesem Zerfall bildet sich eine neue unbekannte Substanz, die sich durch Banden im UR bemerkbar macht, die aber nicht identifiziert werden konnte.

Das BMCP reagiert bereits bei Zimmertemperatur mit NO und auch, etwa 10mal langsamer, mit NO2: (FCO)2O2 + NO → NO2 + CO2 + F2CO bzw. (FCO)2O2 + 2 NO2 → 2 FNO2 + 2 CO2.

Es wird die chemische Analyse des in alkalischer Lösung hydrolysierten BMCP beschrieben.
Beiträge zur Chemie der Bor‐Azide. III. Zur Kenntnis der Pyridinate einiger Bor‐Azide
Authors: Paetzold Peter I.
Published: December 2004

Die Verbindungen Ph2BN3 · Py(I), (n‐C3H7)2BN3 · Py (II) und PhB(N3)2 · Py (III) können durch Azidierung der entsprechenden Chloride mit NaN3 in Pyridin dargestellt werden; ganz analog kann mit LiN3 als Azidierungsmittel B(N3)3 · Py (IV) erhalten werden. Beim thermischen Zerfall von I und II entstehen in einer dem CURTIUS‐Abbau organischer Säureazide analogen Reaktion unter anionischer Wanderung von Phenyl‐ bzw. Propylresten die entsprechenden Borazole. Beim thermischen Zerfall von III bilden sich keine definierten, Bor‐haltigen Produkte.
Absorption Spectra and Stability of Complexes of Transition Metal Ions
Authors: Banerjea D.
Published: December 2004

Using literature data it has been shown that in a majority of analogous complexes of nickel(II) formed by uncharged ligands, which are likely to be octahedral in aqueous solution, the value of log βn (βn being the overall formation constant of the complex being formed from the corresponding hexaquo metal ion and the free ligand) increases linearly with the ligand field splitting parameter, Dq (spectroscopic value).

In case of a series of analogous six‐coordinated copper(II) complexes, by plotting log βn vs. Dq (spectroscopic value), it has been shown that these apparently fall into different groups due possibly to the extent of tetragonal (Jahn‐Teller) distortion being different in each such group.

The anomalous behaviours of bis‐(biguanide)‐nickel(II) and tris(aminoethyl)amine‐copper(II) complexes, which are in conformity with the predictions of the ligand field theory, have also been discussed.
Über das Sulfamido‐acet‐immonium‐chlorid, H3CC(NHCl−)NHSO2NH2 und N‐aminosulfonyl‐acetamidin, H3CC(NH)NHSO2NH2
Authors: Zöllner D. , Meuwsen A.
Published: December 2004

Es wird über die Gewinnung von zwei beständigen Vertretern eines neuen Verbindungstyps(2) berichtet, der sich zugleich vom Sulfuryldiamid, O2S(NH2)2, als auch dem in freiem Zustand wenig bekannten Acetamidin, H3CC(NH)NH2, ableitet.
Mittlere Schwingungsamplituden und UREY‐BRADLEY‐Kraftkonstanten von AsCl und SbCl. Mittlere Schwingungsamplituden von isoelektronischen Ionen
Authors: Nagarajan G. , Müller A.
Published: December 2004

Mit Hilfe der Methode von CYVIN unter Benutzung von Symmetrie‐Koordinaten werden mittlere quadratische Amplituden‐Werte sowie mittlere Schwingungsamplituden für gebundene und nicht gebundene Atome von AsCl und SbCl für 298 und 500°K berechnet. Die Werte für die gebundenen Atome werden im Zusammenhang mit entsprechenden isoelektronischen Ionen verglichen. Hierbei läßt sich zeigen, daß in isoelektronischen Ionen die mittleren Schwingungsamplituden für gebundene Atome mit zunehmender positiver Ladung des Ions abnehmen, während die Valenzkraftkonstanten den umgekehrten Gang zeigen. Weiterhin sind die Kraftkonstanten eines UREY‐BRADLEY‐Potentials und eines einfachen Valenzkraftpotentials berechnet worden.
Über die Vanadate. VIII. Die Bildung von „Bronzen”︁ im AgVO3V2O5‐System
Authors: Lukács I. , Strusievici C. , Liteanu C.
Published: December 2004

Beim Erwärmen von AgVO3V2O5‐Gemischen auf 450–600°C oder Abkühlen ihrer Schmelzen auf 600–500°C bilden sich zwei Phasen von allgemeiner Formel AgxVVOy: die I‐Phase hat x = 0,29–0,43; m = 0,32–0,44; n = 1.56–1,68; y = 4,96–5,05 und entspricht formal einem Ag2(VO)2V10O28; die IIA‐Phase hat x = 0,80–0,99; m = 0,06 bis 0,20; n = 1,80–1,94; y = 5,32–5,46. Diese Phasen unterscheiden sich in den DEBYE‐Aufnahmen und IR‐Absorptionsspektren. Durch Behandlung der IIA‐Phase mit HNO3‐Lösungen wird eine weitere Phase IIB erhalten (x = 0,67–0,77; m = 0,05–0,09; n = 1,91–1,95; y = 5,22 – 5,36), deren Formel angenähert einem Ag4(VO)V10O28 (Unterschuß an V4+) entspricht, und deren Röntgenaufnahme und IR‐Spektrum mit denen der γ‐Phase der Natrium–Vanadin‐„Bronzen”︁ ähnlich ist.
Charge‐Transfer‐Komplexverbindungen des Kupfers. I. Komplexverbindungen des Kupferchlorids mit Diphenylamin
Authors: Spacu P. , Constantinescu O. , Pascaru I. , Brezeanu Maria , Zàlaru Florica
Published: December 2004

Es wurden Komplexverbindungen des Kupferchlorids mit Diphenylamin dargestellt und dabei die Verbindungen mit 1–6 Ligandmolekeln nachgewiesen. Diese Komplexverbindungen wurden im ESR‐Verfahren untersucht; außer dem Signal des Kupfers(II) ermittelte man ein schmales auf den Wert g ∼ 2,00 zentriertes Signal, dessen Intensität mit der Anzahl der Ligandmolekeln in der Komplexverbindung zunimmt. Die ESR‐Spektren sowie ihre Abhängigkeit von der Anzahl der Ligandmolekeln wurden an Hand der Voraussetzung ausgewertet, daß eine molekulare Charge‐Transfer‐Komplexverbindung zugleich mit der stattfindenden Reduktion des Kupfers(II) zu Kupfer(I) entsteht.
Übergangsmetallchalkogenverbindungen. Monothiodiselenomolybdate(VI) und ‐wolframate(VI) Darstellung, Elektronenspektrum und röntgenographische Untersuchung
Authors: Müller A. , Diemann E.
Published: December 2004

Die Darstellung von MMoOSSe2 und MWOSSe2 (MI= Cs, Tl) wird beschrieben. Die gemessenen IR‐ und Elektronenabsorptionsspektren werden diskutiert. Die röntgenographische Untersuchung ergab für die Caesiumsalze, daß sie in der Raumgruppe D—Pnma mit Z = 4 und folgenden Gitterdimensionen kristallisieren:
equation image
.
Die Kristallstruktur von Dicarbonyl‐diacetylbis (dimethylhydrazon)‐Nickel(O)
Authors: Hausen H. D. , Krogmann K.
Published: December 2004

Dicarbonyl‐diacetylbis(dimethylhydrazon)‐Nickel(O) bildet rhombische rubinrote Kristalle der Raumgruppe Pbca. Die Elementarzelle mit den Gitterkonstanten a = 17,91 Å, b = 10,34 Å und c = 14,90 Å enthält acht Moleküle. PATTERSON‐und FOURIER‐Synthesen sowie die Verfeinerung nach der Methode der kleinsten Fehlerquadrate ergaben die Atomlagen bei einem R‐Wert von 11,7%. Jedes Ni‐Atom ist verzerrt tetraedrisch von 2 Carbonylgruppen und dem zweizähnigen organischen Liganden umgeben, der mit dem Zentralatom einen fast ebenen Fünfring bildet.
Der chemische Transport des Silbers mit Jod und die Umkehrung der Transportrichtung im Temperaturgefälle
Authors: Schäfer Harald
Published: December 2004

Die Bildung von Ag3J3,g aus Ag,t + J,g erfolgt exotherm, die entsprechende Bildung von AgJ,g dagegen endotherm. Je nach angewendeter Temperatur ist daher Transport von Ag mit J in die heißere oder in die weniger heiße Zone eines Transportrohres zu erwarten. Die Umkehrung der Transportrichtung wurde thermodynamisch berechnet und experimentell nachgewiesen.
Untersuchung des Systems Silbertellurid‐Silberchlorid
Authors: Bontschewa‐Mladenowa Z. , Aramov N. , Rajkowa D.
Published: December 2004

Das System Ag2TeAgCl wurde mittels differentialthermischer Röntgen‐Phasen‐ und Mikrostrukturanalyse innerhalb des Konzentrationsintervalls von 0 bis 100 Mol‐% Silbertellurid untersucht. Es wurden Gleichgewichtsproben verwendet, welche nach 480stündiger Temperung bei 330°C erhalten wurden. Das System Silbertellurid—Silberchlorid ist eutektisch; eutektischer Punkt bei 80 Mol‐% AgCl und 377°C. Bei 510°C und 33 Mol‐% AgCl wird die Bildung einer Verbindung peritektischen Typs mit der wahrscheinlichen Zusammensetzung Ag5Te2Cl beobachtet.
Über Metallocenborane. II. Mössbauer‐Untersuchungen an Ferrocenylboranen
Authors: Pebler J. , Ruf W. , Siebert W.
Published: December 2004

Mössbauer‐Untersuchungen an Ferrocenyl‐dihalogenboranen (C5H5)‐Fe(C5H4BR2) (R  F, Cl, Br, J) zeigen eine Abnahme der Quadrupolaufspaltung ΔEQ mit zunehmender Lewis‐Acidität der Dihalogenborangruppe. Dagegen bleibt die Isomerieverschiebung δIS konstant.