bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the determination of effective one‐electron Hamiltonians to be used for studying large molecules
Authors: Couty M. , Lévy B. 
Published: December 2004

AbstractWe studied the possibility of defining a one‐electron effective Hamiltonian in the form of a Hückel‐type matrix, taking into account the effect of the environment of the atoms in different molecules (the E2HT). It is found that the appropriate basis set in which this Hamiltonian is defined can be determined by using diatomic fragments. Concerning the matrix elements themselves, the appropriate information can be taken in fragments with a size similar to that of ethane. © 1994 John Wiley & Sons, Inc.
Core photoionization satellites in fullerence and related model systems
Authors: Lunell Sten , Enkvist Christer , Agback Martin , Svensson Svante , Brühwiler Paul A. 
Published: December 2004

AbstractThe so‐called shake‐up satellites accompanying C1s photoionization in C60 have been studied theoretically by means of INDO/CI. It is found that the lowest shake‐up satellites in C60 correspond to global charge‐transfer excitions that move charge from the opposite side of the fullerence cage to the core‐hole region, whereas higher‐energy satellites tend to move charge from regions nearer to the core hole. Analogies are drawn, with, on the one hand, smaller model molecules such as napthalene and acenaphtylene and, on the other hand, infinite systems such as graphite. © 1994 John Wiley & Sons, Inc.
A theoretical approach to the complexation and decomplexation processes in the reaction C60 + He ⇌ (He@C60)
Authors: Xu Zhijin , Yan Jimin 
Published: December 2004

AbstractTo theoretically investigate the complexation and decomplexation processes in the reaction C60 + He ⇌ (He@C60), four possible reaction paths are assumed, so that while He approaches and penetrates the C60 cage (a) a pentagon, (b) a hexagon, (c) a short bond, or (d) a long bond will be expanded on its original sphere or plane to form a window. The computation is performed by the quantum chemical method EHMO/ASED. The results show that the probability of completing this reaction in terms of the tunnel effect can be neglected and the reaction is completed by overcoming a potential barrier of the reaction. It is easily completed by opening a planar window than by opening a shperical window. The probability through reaction path (b) with a barrier of 1247.94 kJ/mol is larger than that through reaction path (a) with a barrier of 1438.26 kJ/mol. The probability through reaction path (d) is the largest with a barrier of 1076.78 kJ/mol, when the planar expansion forming a window of a 9‐membered ring is at the optimized value of 0.40 å. When He deviates the center and approaches the C60 cage, there will be a charge distribution on C60 with changing in size and even in sign along the longitude corresponding to the symmetry axis, but the absolute value gradually decreases. This situation is similar to the charge transfer on carbons in sraight‐chain polyene. © 1995 John Wiley & Sons, Inc.
Characterization of structural transitions from aqueous solution to a lipid phase for α‐MSH
Authors: Jacchieri Saul G. , Ito Amando S. 
Published: December 2004

AbstractFluorescence spectroscopy results show that the α‐melanocyte‐stimulating hormone peptide (α‐MSH) interacts with acidic lipid vesicles. Detectable structural changes are concomitant with the passage of a tryptophan residue from aqueous to lipidic media. The observed multiexponential decay of fluorescence, rationalized as originating from three rotameric populations of the tryptophan residue, has been used together with a matrix algorithm to find the most probable conformational families of α‐MSH in water and lipid environments. A model is discussed in which the same conformational families occur in various phases, although with different probabilities. A conformational family in which χ1 of the Trp9 side chain is in the trans‐rotameric conformation is shown to have structural features highly appropriate to interact with negatively charged biological membranes, which are also in accordance with previous molecular dynamics simulations and with structures engineered in α‐MSH analogs that show an increased potency in biological essays. The gauche minus and gauche plus side‐chain conformations of Trp9, on the other hand, yield conformations more likely to predominate in aqueous solution. NMR spectroscopy measurements of α‐MSH analogs indicate the existence in aqueous solution of a β strand in the vicinity of Trp9. A similar structural feature was found in the present conformational analysis for the gauche minus and gauche plus side‐chain rotamers of Trp9. © 1995 John Wiley & Sons, Inc.
Local quantum chemistry: The local space approximation for Møller–Plesset perturbation theory
Authors: Kirtman Bernard 
Published: December 2004

AbstractThe local space approximation is an accurate technique for describing a relatively small cluster embedded within an extended system. It has previously been developed for the Hartree‐Fock, local density functional, configuration interaction, and coupled cluster electronic structure methods. Here it is extended to Møller‐Plesset perturbation theory. © 1995 John Wiley & Sons, Inc.
Accurate CI expansion in a spline basis of the helium ground‐state wave function
Authors: Decleva Piero , Lisini Adriana , Venuti Marco 
Published: December 2004

AbstractCareful study of radial spline basis‐set convergence on the angular limits of the He 1s 2 state has been performed. Improvement of algorithm allows reaching the full ci limit in a large radial (79 spline functions) and angular (Imax=80) expansion. A variational energy of − 2.903724299061 au, with an error of 7.8 × 10−8 au is obtained, improving by over two orders of magnitude the previous available limit. Accurate angular momentum limits (1 × 10−8 au) are obtained up to l = 25. Analysis of the behavior of two‐particle radial wave functions reveals a sharply peaked behavior which allows effective truncation of the two‐electron radial basis for high angular momentum values. A reasonable estimate of computational resources required indicate that an accuracy below 1 × 10−8 au is presently feasible and about 1 × 10−9 au possible in the near future. © 1995 John Wiley & Sons, Inc.
Theoretical investigation of the conrotatory ring opening of cyclobutene and 1, 2‐dihydro‐1, 2‐diazacyclobutadienes with ab initio and density functional Gaussian‐type‐orbital approach
Authors: Jursic Branko S. , Zdravkovski Zoran 
Published: December 2004

AbstractThe theoretical study of the thermally allowed conrotatory opening of cyclobutene (1) and cis‐ (2) and trans‐1,2‐dihydro‐1,2‐diazacyclobutadiene (3) were performed with ab initio and density functional calculations. The reactants and the transition states were fully optimized by using the 6‐31 + G** basis set with RHF, MP2, SVWN, and BLYP methods. The calculated activation barriers for the ring opening of 1 with both MP2 and SVWN incorporating ZPVF correction give extraordinary agreement with the experimental value. The predicted activation energies for 2 and 3 are lower than in the case of the cyclobutene ring opening. Of the two 1,2‐dihydro‐1,2‐diazacyclobutadiene isomers, the trans isomer has a lower activation barrier. The structural and energy differences and the trend among these compounds are interpreted in terms of orbital overlap and steric interactions in the course of the conrotatory ring opening. © 1995 John Wiley & Sons, Inc.
Real‐space analysis of the exchange‐correlation energy
Authors: Burke Kieron , Perdew John P. 
Published: December 2004

AbstractThe exchange‐correlation energy of a many‐electron system may be written as the electrostatic interaction between the electron density at position r and the density of the exchange‐correlation hole at position r + u. If we average the hole over the entire system, we find that the energy is uniquely decomposed into contributions from various electronic separations u. We may also decompose the hole into contributions from parallel and antiparallel spins. We give several exact conditions which this system‐averaged, spindecomposed exchange‐correlation hole satisfies. Local spin density (LSD) and generalized gradient approximations (GGAS), are more appropriate for u → 0 than for large u and more trustworthy for antiparallel spins than for parallel spins. We illustrate how good LSD is as u = 0 with explicit examples, but also note that, contrary to expectation, LSD is not exact for u=0, except in certain limiting cases. We show that the dramatic failure of the second‐order gradient expansion for large u can be cured by a real‐space cutoff procedure which generates a nonempirical GGA, the Pw91 functional. We conclude with some thoughts about the search for greater accuracy in the next 30 years of density functional theory. © 1995 John Wiley & Sons, Inc.
On the test of different atomic exchange functionals
Authors: Santamaria R. , Kaplan I. G. , Novaro O. 
Published: December 2004

AbstractThe yet unknown exchange‐correlation energy functional and the lack of a systematic way to find such a functional has led to propose different expressions for exchange, on the one hand, and correlation on the other, by several authors. A common factor in the design of exchange functionals is to reproduce different kinds of energies rather than the important atomic shell structure. We present a strategy for testing the behavior of exchange functionals based on the reproduction of atomic shell structure. A variety of well‐known exchange functionals are tested on He (closed shell), Li (open shell), and Be (closed subshell). Important differences are found among them. Finally, we propose an exchange energy functional that includes a Becke‐88‐type expression and, in addition, a nongradient correction term that leads to improved shell structure behavior. © 1995 John Wiley & Sons, Inc.
Density functional LCAO calculations for solids: Comparison among Hartree–Fock, DFT local density approximation, and DFT generalized gradient approximation structural properties
Authors: Zupan Aleš , Causà Mauro 
Published: December 2004

AbstractIn this article, the results of a recently implemented DFT a posteriori and Kohn‐Sham (KS) linear combination of atomic orbital computational scheme for solids are presented. The equilibrium lattice parameters, bulk moduli, and lattice energies are calculated for eight crystallized systems. Local density approximation (LDA) and generalized gradient approximation (GCA) functionals and potentials are used. The maps of the Hartree‐Fock (HF) and Ks electronic densities and band structures are depicted. The KS results confirm the trend of the a posteriori scheme. Very good agreement between calculated and experimental lattice energies has been found for GGA potentials. © 1995 John Wiley & Sons, Inc.
On the gradient expansion of the exchange energy within linear response theory and beyond
Authors: Svendsen P. S. , Von Barth U. 
Published: December 2004

AbstractIn the present work, we reexamined the gradient expansion of the exchange energy of an electron gas with a slowly varying charge density. We stay within the exchange‐only approximation of Sharp, Horton, Talman, and Shadwick but go to second order in the deviation from the homogeneous limit. The coefficient of the lowest‐order gradient correction is obtained analytically both for a bare and a screened Coulomb interaction—the former yielding the value previously obtained by Kleinman numerically and by Engel and Vosko analytically. A screened Coulomb interaction gives Sham's coefficient in the limit of infinite screening length. The cause of the difference between the coefficients of Kleinman and Sham is clearly exhibited. The coefficients of the two next highest‐order gradient corrections, one of which originates in second‐order response theory, is shown to diverge as the screening length becomes large. The bare Coulomb interaction gives finite coefficients of which the one originating from linear response is obtained analytically and differs from the presumably correct result obtained by Engel and Vosko. This discrepancy demonstrates the extreme sensitivity of the analytical expressions to different regularization procedures. We suggest that coefficients should rather be chosen according to the performance of the resulting gradient approximations in weakly perturbed electron gases. © 1995 John Wiley & Sons, Inc.
A nonequilibrium time‐dependent functional theory based on Liouvillean quantum field dynamics
Authors: Rajagopal A. K. , Buot F. A. 
Published: December 2004

AbstractA brief description of an extension of the time‐dependent functional theory to coupled field systems such as electron‐ion and electron–electromagnetic fields is given. This theory is further generalized to situations where the system is initially in thermodynamic equilibrium and is subjected to external time‐dependent probes which may drive the system out of equilibrium. Such a generalization is based on the Liouvillean quantum field dynamics (LQFD). The above formalism provides a firm physical and mathematical basis for time‐dependent simulation procedures such as those based on the Car–Parrinello approach by replacing the fictitious Lagrangian by a precise action principle. Several physical examples are given to illustrate the need for this formalism, where there is a necessity for treating all the field variables on equal footing and in a self‐consistent way. A new alternate formalism of time‐dependent functional theory based on a novel application of the Baym Φ‐derivable method is also given in terms of LQFD. By choosing suitable processes to set up the (D‐functional, our functional theory is transformed into a practical self‐consistent approach to the quantum many‐body equilibrium and transport problems, with built‐in conservation laws for all the physically relevant variables). © 1995 John Wiley & Sons, Inc.
Fermi and Coulomb holes of molecules in excited states
Authors: Wang Jiahu , Smith Vedene H. 
Published: December 2004

AbstractCorrelation holes of electrons with the same (Fermi hole) and different (Coulomb hole) spins in the ground (X1Σ+), first (A1Σ+) and second (B1II) excited states of LiH were constructed from full configuration interaction (CI) wave functions. It was found that the shapes of both the Fermi and Coulomb holes in these states are dependent on the location of the reference electron. When the reference electron is chosen to be close to the Li nucleus, the Fermi correlation results in a large negative hole for all three states. However, the A1Σ+ excited state is further characterized by displaying a second hole around the H nucleus, and in the B1II state, the hole is elongated along the molecular axis. Coulomb correlation shows up strongly in the A1Σ+ state and, in addition, there is clearly correlation of electrons at the two nuclei. These features of the correlation holes were compared with those from a two‐Slater‐determinant model wave function. The Hartree, Fermi, and Coulomb screening potentials in these states were also studied in the light of possible modeling of the correlation functionals for the excited states. © 1995 John Wiley & Sons, Inc.
Sputtering of metals with 20 keV O: Characteristic etch patterns and sputtered atom yields
Authors: Tsunoyama K. , Suzuki T. , Ohashi Y. , Kishidaka H. 
Published: December 2004

AbstractThe surface structures of polycrystalline pure metals bombarded with 20 ke V O+2 were observed by a SEM and their sputtered atom yields obtained by measuring the depth of crater with an interferoscope. The etch patterns produced were classified according to the binding energy of mono‐oxide BMO of the target atom M and an oxygen atom; the surface become smooth as the binding energy increased. The sputtered atom yield showed similar periodicity to those obtained by noble gas ion bombardment. It was therefore concluded that the sputtered atom yield was primarily determined by physical collision of atoms in the target material and was not affected very much by the chemical reaction of implanted oxygen atoms.
A simple digital inelastic electron tunnelling spectrometer
Authors: Reynolds S. , Gregson L. D. , Horley C. C. , Oxley D. P. , Pritchard R. G. 
Published: December 2004

AbstractA modified inelastic electron tunnelling spectrometer is described which enables data to be stored in digital form in a microcomputer. Subsequent numerical analysis may then be carried out with considerable flexibility and convenience. Presentation of data is possible, not only in second derivative form as in a conventional spectrometer, but also as a third derivative by a simple numerical technique. Examples of data presented in both forms are given for a tunnel junction consisting of Al/AlOx/benzoic acid/Pb. In addition, the third derivative technique is used to subtract a rising background from the second derivative spectrum of an Al/AIOx/benzoic acid/Au tunnel junction.
The angular dependence on photoemission and its significance to quantitative surface analysis by XPS
Authors: Vulli M. 
Published: December 2004

AbstractAn attempt is made in the present work to determine experimentally the asymmetry parameter β for electrons with various angular momenta from solid samples. This method is somewhat more complicated than that for determining β from gaseous samples. The β values obtained, for instance for Cu 2p, are β = 1.86 and 1.34 by using for A1 Kα and Mg Kα excitation radiations respectively. The corresponding theoretical values are β = 1.42 and 1.32. Examples are also given for the significance of the anisotropic angular distribution to quantitative surface analysis.
Surface analysis of sulfided dispersed metal catalysts
Authors: Reucroft P. J. , Shalvoy R. B. 
Published: December 2004

AbstractA Ni–Cr/MgSiO3 catalyst retained appreciable methanation activity after a pre‐sulfiding treatment in comparison with Ni/MgSiO3 catalyst. Surface analysis by X‐ray photoelectron spectroscopy of pre‐sulfided catalysts that have been treated in various ways has shown that the Ni–Cr/MgSiO3 catalyst retains less total sulfur and that the sulfur retained is in the form of both sulfide and sulfate. In the Ni/MgSiO3 catalyst, sulfur is found only in the sulfide form. It is proposed that the presence of Cr (as Cr2O3) promotes the formation of sulfate which deactivates the catalyst to a lesser extent due to the instability of the sulfate ion at the methanation reaction temperature.
The effects of functional group mobility on quantitative ESCA of plasma modified polymer surfaces
Authors: Everhart D. S. , Reilley C. N. 
Published: December 2004

AbstractWetting nitrogen plasma modified polyethylene with a permeable solvent rapidly reduces the surface concentration of amines originally incorporated with plasma exposure. The rate of decrease in surface amine concentration increases with increasing hydrogen bonding capabilities of the solvent. A slower decrease in the surface amine concentration occurs for dry, modified polymers not wet with a solvent. A model consistent with a solvent mediated dilution of surface groups into the interior of the polymer is proposed. Upon protonation with aqueous H3PO4 or H2SO4, subsurface amines readily migrate back to the surface; HCl and HNO3 do not produce this result. The rate of concentration of protonated amines into the ESCA sampling depth is dependent on the permeability of the aqueous acid and the solubility of the corresponding protonated ammonium salt in polyethylene. The mobility of surface functional groups seriously affects the use of chemical derivatization reagents for the ESCA of modified polymer surfaces and raises important questions concerning the significance of a polymer surface analysis. The reaction of surface amines with pentafluorobenzaldehyde is used to illustrate this point.
Oxidation of surface‐treated SiC platelets studied by XPS and bremsstrahlung‐excited AES
Authors: Wang Pu Sen , Malghan Subhas G. , Hsu Stephen M. , Wittberg Thomas N. 
Published: December 2004

AbstractX‐ray photoelectron spectroscopy (XPS) and bremsstrahlung‐excited Auger electron spectroscopy (AES) were used to study the oxidation of treated silicon carbide platelets heated in air at 700, 800 and 850°C. A previous study had shown that when the as‐received silicon carbide platelets were heated in air, boron segregated to the surface during the formation of the oxide scale. Boron is present as a minor impurity in the silicon carbide platelets. The oxidation was found to be non‐linear and non‐parabolic. In the present study, the silicon carbide platelets were treated by heating in air at 800°C and then etching off the surface oxide scale with 30% HF. This procedure removed the boron impurity. The oxidation of these treated silicon carbide platelets was found to be linear in the temperature range 700–850°C. The activation energy was measured to be 63 ± 12 kJ mol−1 (15 ± 3 kcal mol−1). These results are in very good agreement with previous results for SiC whiskers. No boron was detected during the oxidation of the treated SiC platelets.
Surface study of DWA‐wetted TiO2 pigments
Authors: Johansson Leena‐Sisko , Losoi Tuomo , Juhanoja Jyrki 
Published: December 2004

AbstractWe present a study on the dispersion of coated TiO2 pigments in acrylic‐isocyanate automotive paints, based both on the surface characterization of the pigment particles and on studies of the films prepared from the paint. We investigated how the Al2O3–SiO2 coating on TiO2 affects the adsorption of an organic dispersing and wetting agent (DWA) and what the effect of this surfactant is on the dispersibility of the pigment. The study also shows the value of surface methods in the characterization of powder surfaces.Five Al2O3‐ and/or SiO2‐ coated TiO2 pigment samples were used as substrates. These were treated with varying amounts of a commercial organic DWA. The substrate surfaces were characterized with XPS and zeta potential measurements prior to the DWA treatment. The adsorption of the surfactant was analysed with carbon analysis, UV and IR spectroscopies, XPS techniques and with static SIMS. Results from both the XPS analyses and adsorption measurements showed that the substrate saturation point for DWA depended on the pigment surface, owing to variations in substrate acidity.The effect of the DWA treatment on pigment dispersion was studied in paints. The TiO2 pigments with and without the treatment were dispersed in acrylic‐isocyanate automotive paints together with a DWA‐wetted red pigment. The TiO2 dispersion from the paint films was studied with a mechanical rub‐out test, x‐ray microanalysis and XPS sputter profiling. The observed colour variations in rub‐out tests were clearly connected with DWA treatment. X‐ray microanalysis revealed differences in the TiO2 pigment dispersion stage that probably caused these variations.
Determination of overlayer thickness by angle‐resolved XPS: A comparison of algorithms
Authors: Fulghum Julia E. 
Published: December 2004

AbstractAngle‐resolved XPS data from two well‐characterized samples of SiO2 on Si were analyzed using three different algorithms for the determination of overlayer thickness. The relative ratio algorithm, the Heaviside step function approximation to the Laplace transform algorithm and the absolute ratio algorithm were compared in terms of the d/λ values calculated, correlated parameters, experimental requirements, goodness‐of‐fit and sensitivity to overlayer thickness variation. Although an inverse correlation exists between the normalization parameter and d/λ for the relative ratio algorithm, this algorithm is recommended over the absolute ratio algorithm and the Laplace transform algorithm for the determination of overlayer thicknesses. The relative ratio algorithm results in the most accurate overlayer thickness ratio and is more sensitive to overlayer thickness variations than the other algorithms.