bluuebunny/crossref_metadata_2025_split huggingface dataset:
A comparative study on the structure of M2Se and M2I+ (M = Ag, Au) using pseudopotentials and full Ab initio methods
Authors: Alemany Pere , Novoa Juan J. , Bengtsson Lars 
Published: December 2004

AbstractThe molecules of M2Se and M2I+ (M = Ag, Au) are used as test models to study the quality of the pseudopotential methodology when using the Hartree–Fock and second‐order Møller‐Plesset methods. We have used two implementations of the Wadt and Hay pseudopotentials: the new large‐ and small‐core pseudopotentials (known as LANL 1DZ and LANL2DZ in GAUSSIAN‐92) and the traditional one used for a long time. It is found that the optimum geometry depends on the type of pseudopotential selected. A comparison with the results computed when all the electrons are taken explicitly into account shows that the new LANL1DZ and LANL2DZ give the right answer. Using these potentials, the geometry and potential energy surface of the M2Se and M2I+ systems is explored and its optimum geometry found. © 1994 John Wiley & Sons, Inc.
Dynamics of photochemical reactions: Simulation by quantum calculations for transition metal hydrides
Authors: Daniel C. , Heitz M. C. , Lehr L. , Schröder T. , Warmuth B. 
Published: December 2004

AbstractThe photodissociation dynamics of some organometallic molecules in the lowest repulsive electronically states are reported for the following concurrent primary reactions: (i) the homolysis of a metal–hydrogen bond vs. the heterolytic loss of a carbonyl ligand in HCo(CO)4; (ii) the photoinduced elimination of molecular hydrogen vs. the loss of a carbonyl ligand in H2Fe(CO)4; and (iii) the photoinduced elimination of molecular hydrogen vs. the loss of a mesithylene ligand in H2Os(CO)Mes (Mes = C6H3(CH3))3. The dynamics are simulated quantum mechanically using a time‐dependent wavepacket propagation technique on potential energy surfaces obtained from CASSCF/CCI calculations for HCo(CO)4 and H2Fe(CO)4 and from SCF‐INO/MRCI calculations for H2Os(CO)Mes. This approach gives a rather detailed view of some important elementary processes that contribute to the photochemistry of these complexes. The nature of the photoactive excited states is determined without ambiguity, as well as the time scales, the branching ratio of the different primary dissociation pathways, and some features of the absorption spectra. © 1994 John Wiley & Sons, Inc.
Application of many‐body perturbation theory in the localized representation for the all‐trans conjugated polyenes
Authors: Kapuy E. , Bogár F. , Tfirst E. 
Published: December 2004

AbstractAb initio self‐consistent field (SCF) calculations are performed with the standard 6‐31G* basis set for all‐trans conjugated oligomers C2n+2H2n+4. The canonical occupied and virtual molecular orbitals (MOs) are separately localized by unitary transformations. Due to the localization, the perturbation operator is partitioned into two‐particle and into single‐particle terms; the MBPT is, therefore, a double‐perturbation expansion in this case. By using the localized representation of the MBPT, the correlation energy contributions can be partitioned into local and nonlocal effects. It can be shown that the local effects are very important and well transferable, which makes possible the calculation of the correlation energy of larger molecules if the localized molecular orbitals (occupied and virtual) of smaller related molecules are known. © 1994 John Wiley & Sons, Inc.
On the accuracy of molecular properties by coupled‐cluster methods for some difficult examples: Oxygen atom, iron atom, and cyano radical
Authors: Urban Miroslav , Watts John D. , Bartlett Rodney J. 
Published: December 2004

AbstractCoupled‐cluster (CC) methods at the level of CCSD, CCSD+T(CCSD), CCSD(T), CCSDT‐1, and CCSDT‐3 are applied to calculations of the dipole moment and polarizability of the CN molecule, ionization potentials and electron affinities of the oxygen and iron atoms and CN molecule, and the energy splitting of the 5D and 5F states of the iron atom. Both UHF and ROHF references are applied. Extended basis sets are used in some comparison of CC data to experiment. All calculated atomic and molecular properties are known as challenging problems, suitable for a careful analysis of the performance of sophisticated versions of the CC approach. Attention is paid to energy terms distinguishing CCSD(T) from CCSD+T(CCSD). We exploit results from various iterative and noniterative high‐level CC methods in the assessment of error bars in calculations of atomic and molecular properties. © 1994 John Wiley & Sons, Inc.
Extrapolation of real‐space quantum chemical calculations from finite‐size super cells to the ideal infinite system. II. Application to one‐dimensional polymers
Authors: Nolting V. , Verwoerd W. S. 
Published: December 2004

AbstractCalculations of finite atomic clusters based on the Hartree–Fock self‐consistent field theory are modified to model more closely the ideal behavior of the infinite system. The density matrix of the standard finite supercell calculation is extrapolated to an infinite supercell so that it contains information from a continuum of k points in the first Brillouin zone. This modification is incorporated into the self‐consistency loop of the MOPAC quantum chemistry program and leads to improved results compared to a standard finite supercell calculation. Heats of formation, bond lenghts, and electronic properties converge more quickly to the correct ground‐state values. For polyacetylene, we obtain a reduced bond‐length alternation of Δr = 0.084 Å, which is in agreement with more sophisticated calculations containing electron correlation effects. © 1994 John Wiley & Sons, Inc.
On a generalized Kepler–Coulomb system: Interbasis expansions
Authors: Kibler M. , Mardoyan L. G. , Pogosyan G. S. 
Published: December 2004

AbstractThis article deals with a dynamical system that generalizes the Kepler–Coulomb system and the Hartmann system. It is shown that the Schrödinger equation for this generalized Kepler–Coulomb system can be separated in prolate spheroidal coordinates. The coefficients of the interbasis expansions between three bases (spherical, parabolic, and spheroidal) are studied in detail. It is found that the coefficients for the expansion of the parabolic basis in terms of the spherical basis, and vica versa, can be expressed through the Clebsch–Gorden coefficients for the group SU(2) analytically continued to real values of their arguments. The coefficients for the expansions of the spheroidal basis in terms of the spherical and parabolic bases are proved to satisfy three‐term recursion relations. © 1994 John Wiley & Sons, Inc.
Role of tunneling of hydrogen in photoenolization of a ketone
Authors: Sengupta Debasis , Chandra A. K. 
Published: December 2004

AbstractPhotoenolization of a ketone in its lowest triplet state was examined using the AM1 semiempirical molecular orbital method with complete geometry optimization at the configuration interaction level in the restricted Hartree–Fock frame. The theoretical barrier fits with a polynomial given by Eq. (1) and the probability of tunneling of hydrogen was calculated by the WKB method. The density of states above the zero‐point level was estimated by the Whitten–Rabinovitch approximation. Rate constants for the hydrogen and deuterium‐abstraction processes via tunneling were then computed at different temperatures. © 1994 John Wiley & Sons, Inc.
A semiclassical density functional evaluation of the smoothly varying part of the Hartree–Fock binding energy in atoms
Authors: Delchev Ya. I. , Pavlov R. L. , Pavlova A. , Marinova L. P. , Maruani Jean 
Published: December 2004

AbstractA semiclassical density functional approach is used to evaluate the smooth part of the variation of the Hartree–Fock (HF) binding energy in atoms, from helium through xenon. The energy density functional is chosen with an improved form for the kinetic energy functional (KEF). The variation of the HF binding energy is split into smooth and oscillating (shell‐structure) parts, in accordance with Strutinskyøs self‐consistent averaging procedure, which is equivalent to a semiclassical ħ‐expansion of the KEF. This enables a well‐grounded evaluation of the oscillating part of the HF binding energy, which displays a quasi‐periodic behavior expressing clearly the shell structure of atoms. © 1994 John Wiley & Sons, Inc.
Stationary response with exponential transformation: A perturbative analysis for molecular static properties
Authors: Ghose Keya Basu 
Published: December 2004

AbstractWe present here a perturbative analysis of the coupled cluster response method for molecular static properties with Euler and extended coupled cluster functionals under cubic truncation. Comparative analysis is meant to cater to both pedagogical and practical interests. Comprehensive tables for energy‐derivative expressions and equations at the stationary point are presented. © 1995 John Wiley & Sons, Inc.
The interaction of chemical bonds. IV. Interbond charge transfer by a coupled‐cluster‐type formalism
Authors: Surján Péter R. 
Published: December 2004

AbstractA fully linearized coupled‐cluster technique is used to improve a multiconfigurational wave function. The reference function is constructed as the antisymmetrized product of strictly localized geminals. The matrix elements appearing in the formalism are trivial to evaluate. The form of the cluster operator is chosen to produce one‐electron transfer from one geminal to another. The method is tested on the He ⃛ He potential curve. It is found that the importance of such charge‐transfer contributions is the same as that of dispersion. Clusters of three He atoms are also examined and some illustrative calculations on small molecules are presented. © 1995 John Wiley & Sons, Inc.
A formulation of multiple‐reference CI with terms linear in the interelectronic distances. II. An alternative ansatz
Authors: Gdanitz Robert J. , Röhse Robert 
Published: December 2004

AbstractAn alternative ansatz for r12‐MR‐CI is given. The final formulas are much more easily obtained than was possible previously. The numerical performance is demonstrated with a model calculation of the ground state of helium using three different Gaussian basis sets (5s, 10s, 16s). With the two largest basis sets, the energies obtained with the new formulas, the formulas of Part I of this series of articles, and the formulas of the original formulation agree within 2 μEH. Since the new ansatz is much easier to handle mathematically, we recommend its usage for future work. © 1995 John Wiley & Sons, Inc.
Evaluating the performance of correlated methods in molecular property calculations: Pattern recognition and clustering in spaces of theoretical descriptions
Authors: Maroulis George 
Published: December 2004

AbstractA rigorous approach to the evaluation of the performance of correlated methods in molecular property calculations is proposed. Theoretical descriptions of molecules are identified as collections of molecular property values. Distance functions are then defined in the space of theoretical descriptions and the metric properties are used to define proximity and similarity between theoretical descriptions. Graph theoretic arguments and pattern recognition techniques are used to study ordering, classification, self‐organization, and clustering in the space of theoretical descriptions. © 1995 John Wiley & Sons, Inc.
Performance of valence‐universal multireference coupled‐cluster theory for quasi‐degenerate states: The H8 and DZPH4 models
Authors: Jankowski K. , Grabowski I. 
Published: December 2004

AbstractValence‐universal coupled‐cluster (VU–CC) methods corresponding to the approximations S ≃ S1 + S2 (VU–CCSD) and S ≃ S1 + S2 + S3 (VU–CCSDT) for the cluster operator S have been applied to two model systems for which the degree of quasi‐degeneracy of the two lowest, totally symmetric, singlet states may be varied over a wide range by changing their geometry. The performance of the VU–CC methods is investigated with the aim of verifying the findings of recent extensive reliability studies of these methods [Jankowski et al., J. Chem. Phys. 97, 7600 (1992); Ibid. 101, 3085 (1994)] based on calculations for the less complex minimum basis set H4 model. The present results confirm these findings. In particular, the VU–CCSD energies are less accurate than those obtained with other single‐ and multireference methods including up two‐body amplitudes. It is also confirmed that the impact of the S3 clusters is significant and the accuracy of description is rather insensitive to the kind of molecular orbitals employed. © 1995 John Wiley & Sons, Inc.
Chemistry and the near‐sighted nature of the one‐electron density matrix
Authors: Bader Richard F. W. 
Published: December 2004

AbstractTwo different macrospopic pieces of copper have different external potentials and, because of the unique functional relationship between the electron density and the external potential as demanded by density functional theory, should possess different electron density distributions. Experimentally, however, an atom in the bulk exhibits the same electron density in both samples and they possess identical sets of intensive properties. Density functional theory does not account for the fundamental observation underlying the theory of atoms in molecules: that what are apparently identical distributions of charge can be observed for an atom or a grouping of atoms in systems with different external potentials and that these atoms contribute essentially identical amounts to the energies and all other properties of the systems in which they occur. It is shown that, unlike the external potential, the kinetic energy density and the potential energy density, defined by the virial of the Ehrenfest force acting on electron density, are short‐range functions. As recorded in the first article on atoms in molecules, they exhibit a local dependence on the electron density that causes them to faithfully mimic the transferability of the atomic charge distributions from one system to another. The electron, the kinetic energy, and the virial densities are all determined directly by the one‐electron density matrix, a function termed near‐sighted by Professor Kohn. It is this near‐sighted property of the one‐matrix that underlies the working hypothesis of chemistry—that of a functional group exhibiting a characteristic set of properties. The observations obtained from the theory of atoms in molecules and the atomic theorems it determines demonstrate the existence of a local relationship between the electron density and all properties of a system. © 1995 John Wiley & Sons, Inc.
Modeling of the mutual molecular polarization with an electronegativity equalization approach
Authors: Gerwens Heiko , Jug Karl 
Published: December 2004

AbstractA model for the mutual polarization of two approaching molecules is proposed, exploiting the principle of electronegativity equalization. The deformation of the electronic density of one molecule is the response to the perturbation of its chemical potential due to the electrostatic potential of the other molecule. The electronic densities, the density deformations, and the electrostatic potentials of both molecules are described with a previously developed asymptotic density model (ADM). TheADMmodel allows a partitioning of all relevant properties in terms of atomic quantities. The perturbation of the chemical potential is given in atomic resolution, and the change of the electronic density is represented in terms of atomic charges. A hardness tensor, which determines the changes of the atomic chemical potentials due to the changes of the atomic charges, is modeled consistently with theADMand earlier approaches. The results of the model, the changes of atomic charges within the molecules due to their mutual interaction, are compared with the changes of atomic charges obtained from population analysis of ab initio calculations. © 1995 John Wiley & Sons, Inc.
The effect of source window material and thickness on the intensity of moderated positrons
Authors: Hulett L. D. , Dale J. M. , Pendyala S. 
Published: December 2004

AbstractWhen fast positrons from a radioactive source such as 58Co or 22Na are impinged on a suitably prepared moderator surface a measurable fraction (∼0.1%) is re‐emitted as a monoenergetic beam. Several groups have efforts underway to implement this phenomenon as a practical monoenergetic positron gun to be used for surface studies. To address the question that arises about the effects of the window of the capsule that contains the fast positron source, moderated positron intensities have been measured for windows constructed of several different materials of varying thicknesses. A semilog plot of the data approximates a universal curve, with all points on the same line regardless of material. A 58Co source can be masked by windows as thick as 22 µm Al or 11 µm Ti without decresasing the moderated positron intensity by more than 35%. Since 22Na has a similar fast β+ spectrum we have the implication that window effects for sources of this material will be of the same degree.
Dependence of surface composition of ZrNi intermetallic compounds on their bulk composition and heat treatment
Authors: Nefedov V. I. , Lunin V. V. , Chulkov N. G. 
Published: December 2004

AbstractX‐ray photoelectron spectroscopy (ESCA) was used to study the dependence of Zr2Ni, ZrNi and ZrNi5 intermetallic compound surface compositions upon duration of heating in air at 200 °C. The changes in relative intensities of Zr 3d, Ni 3p and Ni 2p lines in the course of ion sputtering and their dependences on take‐off angle of photoelectrons were measured. The post‐oxidation surface composition was: Ni (NiO) in the uppermost layer, its content increased with the time of heating. The following layer was enriched with ZrO2. The minimum of Ni/Zr atomic ratio was observed for 10–40 Å depth, depending on intermetallic compound composition and heating time. The next layer was enriched with Ni and for 1000–1600 Å depth the stoichiometric bulk composition was attained. The formation of a Ni rich layer over ZrO2 is explained by Ni diffusion through the oxide film.
Study of relative thickness of thin oxide layers at Si3N3/Si interface by auger depth profiling
Authors: Pan Paihung , Velasquez Peter C. , Douse Richard W. 
Published: December 2004

AbstractAuger depth profiles of nitride—oxide—silicon (NOS) structures with oxide thickness of 27.4 Å, 31.4 Å, 41.7 Å and 52.5 Å have been studied. The area under the oxygen peak‐to‐peak trace was found to depend on the thickness, d, and the sputtering rate, R, of the oxide layer. A simple equation has been derived, showing that the area is proportional to d/R. The experimental data agree with the derived equation.
Quantitative thin‐film analysis with an energy‐dispersive x‐ray detector
Authors: Waldo Richard A. , Militello Maria C. , Gaarenstroom Stephen W. 
Published: December 2004

AbstractRecent mathematical approximations of ϕ(ρz), the depth distribution of electron‐excited x‐rays, have opened up the possibility of accurate quantitative analysis of thin‐film specimens by electron beam techniques. This method has been used extensively in electron probe microanalysis. This paper demonstrates quantitative analyses of thin films using energy‐dispersive x‐ray analysis (EDS) coupled with the ϕ(ρz) method. Metal and oxide films were analyzed by several techniques, including electron probe microanalysis (EPMA), Rutherford backscattering spectroscopy (RBS), x‐ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), spectroscopic ellipsometry (SE) and x‐ray fluorescence spectroscopy (XRF); the results were compared with those obtained from the EDS thin‐film analysis. In the case of Al2O3 films, EDS film thickness results agree to within ±4%, ±7% and ±9% of the TEM, EPMA and SE results, respectively. For metal films, the EDS results agree to within ±12% (thicknesses) and ±7% (composition) of the RBS, EPMA and XRF results.
Quantitative XPS. Part II: Comparison between different quantitative approaches for two different spectrometers—determination of the contamination‐reduced thickness, application of the determined transmission functions and accuracy achieved
Authors: Weng L. T. , Vereecke G. , Genet M. J. , Rouxhet P. G. , Stone‐Masui J. H. , Bertrand P. , Stone W. E. E. 
Published: December 2004

AbstractThe first principles model (FPM) has been compared with other quantitative approaches by using many standard samples. As a first step, the applicability of the theoretical dependence of IC 1s/ICKVV on the reduced thickness (x) of a hydrocarbon surface contamination layer was checked and shown to be approximately correct only in the middle range of x. A semi‐empirical relation between IC 1s/ICKVV and x has been developed. The advantage of this relation over that previously developed in the literature is that the transmission function of our spectrometer is well characterized. The reduced thickness calculated using this semi‐empirical relation has been shown to be close to the real value. The comparison of atomic ratios calculated using these quantitative approaches has shown that the best approach is the FPM. For the samples investigated in this work, the introduction of the anisotropy parameter L is not necessary: in most cases, the influence of L is smaller than the observed errors; and in certain cases where the difference of L values is large, more consistent results are obtained when L is ignored. The FPM approach provides consistent results not only when an inter‐comparison is made between different spectrometers but also when, within a given machine, the analysis conditions are varied. The accuracy of this approach is relatively good (with errors <15%) and holds true even when comparing peaks separated by more than 1000 eV. Finally, the comparison of results obtained with different previously determined transmission functions has allowed us to test the applicability of the methods used for the determination of these transmission functions (see Part I).
Quantitative study of background signals from crater edges and surroundings in depth profiling of small areas with secondary ion mass spectrometry
Authors: Meuris M. , De Bisschop P. , Vandervorst W. 
Published: December 2004

AbstractA theoretical model is presented to calculate the redeposition of ions and neutrals generated during sputter bombardment in a secondary ion mass spectrometry (SIMS) measurement. This model is compared with measurements of boron in silicon in an on‐chip geometry, i.e. the analysis of low doping levels of an impurity in an area surrounded by a region that contains high amounts of this impurity. The present results indicate that the ion acceptance profile of the secondary ion beam and the redeposition of ions and neutrals generated during the sputtering form the limiting factors in small‐area on‐chip analysis. The non‐ideal definition of the acceptance profile is solved by superimposing an electronic gate onto the optical gate of the instrument. For the analysis of B in Si and Si in GaAs and AlxGa1−xAs, the use of Cs+ reduces the background signal of the measurement compared with O2+.
Exact analytical solutions and close approximations to the depth distribution function in AES and XPS
Authors: Dwyer V. M. , Richards J. M. 
Published: December 2004

AbstractThis paper presents an analysis of the form of the depth distribution function (DDF) for one of the only scattering cross‐sections for which a solution to the Boltzmann transport equation (BTE) is readily available. In doing so we demonstrate how different approximations lead to DDFs of differing complexity. The possibility of achieving the requirement for quantitative AES and XPS of a simple yet accurate DDF is discussed.