bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Principle of maximum physical hardness
Authors: Pearson Ralph G. 
Published: December 2004

AbstractThe proof of Parr and Chattaraj for the Principle of Maximum Chemical Hardness is very general and can be applied to many more observables. The case of the physical, or mechanical, hardness of a solid is taken as an example. It is shown that this also should be a maximum in an equilibrium system. Assuming the validity of the argument leads to new information about the compressibility of solids. A simple expression is also given for the Gruneisen constant. These maximum principles are necessary consequences of the equilibrium conditions of quantum mechanics and thermodynamics. © 1995 John Wiley & Sons, Inc.
Density functional theory for systems of very many atoms
Authors: Kohn W. 
Published: December 2004

AbstractThe standard Kohn‐Sham formulation of density functional theory (DFT) is limited, for practical reasons, to systems of less than about 50‐100 atoms. The computational effort scales as N, where Nat is the number of atoms and 2 < α > 3. (By comparison, conventional configuration interaction methods are limited to 5‐10 atom systems.) This article deals with the prospect of practical methods that scale linearly in Nat and may thus allow calculations for systems of 103‐104 atoms. The physical reason (“near‐sightedness”) for linear scaling is presented. Implementations of linear scaling DFT by the use of generalized Wannier functions or the one‐particle density matrix are discussed. © 1995 John Wiley & Sons, Inc.
Density functionals for the Yukawa electron‐electron interaction
Authors: Savin Andreas , Flad Heinz‐Jürgen 
Published: December 2004

AbstractShort‐range nonclassical electron‐electron interaction is described by a density functional in a scheme that allows multideterminant wave functions. The parameter that determines the coupling with the configuration‐interaction‐type calculations can be chosen in a controlled manner. Results are presented for the He and the Be series using a Yukawa‐type interaction. © 1995 John Wiley & Sons, Inc.
Some efforts beyond the local density approximation
Authors: Sham L. J. 
Published: December 2004

AbstractThe exchange‐correlation density functional can be expressed as a many‐body perturbation series in terms of the Coulomb interaction using the exact Kohn‐Sham orbitals as the basis. A self‐consistent equation is derived for the exact exchangecorrelation potential. This perturbation approach forms a basis for going beyond the local density approximation (LDA). The discontinuity in the exchange‐correlation potential for semiconductors calculated by the perturbative approach gives a good account of the discrepancy of the band gap calculated in LDA. The discontinuity also plays an important role in the interface band diagrams. A theory to account for the interaction effects of localized d or f orbitals is reviewed and the physics of the applications to a model test, to some 3d transition metals, and to heavy fermions is discussed. The perturbative approach to improvement beyond LDA tends to be computation‐intensive and to be system‐specific. © 1995 John Wiley & Sons, Inc.
Exact theorems concerning noninteracting kinetic energy density functional in D dimensions and their implications for gradient expansions
Authors: Holas A. , March N. H. 
Published: December 2004

AbstractThe focal point of the present work is the single‐particle kinetic energy density tensor in D dimensions. This quantity enters both differential and various integral forms of the virial theorems, which are again set up in D dimensions. Major new results lie in (i) demonstrating that, by one‐dimensional quadrature, it is possible to construct the Pauli potential directly from the kinetic energy tensor, without the need for functional differentiation and (ii) generating the gradient expansion for the kinetic energy tensor, in D dimensions. © 1995 John Wiley & Sons, Inc.
New exact relations for improving the exchange and correlation potentials
Authors: Levy Mel , Görling Andreas 
Published: December 2004

AbstractFor the purpose of improving present approximations to the exchange and correlation potentials, newly derived properties of the exact exchange and correlation potentials are summarized. Present approximations are not expected to generally satisfy these properties. The summarized properties include relations at the Fermi level, low‐density requirements, and a new density functional formula for computing ionization energies. © 1995 John Wiley & Sons, Inc.
Average local electrostatic potential and the core‐valency separation in atoms
Authors: Sen K. D. , Gayatri T. V. , Krishnaveni R. , Kakkar M. , Toufar Helge , Janssens Geert O. A. , Baekelandt Bart G. , Schoonheydt Robert A. , Mortier Wilfried J. 
Published: December 2004

AbstractThe average local electrostatic potential function, V(r)/ ρ(r), is calculated for 87 atoms, Li‐Ac, in the ground state using the nonrelativistic average‐over‐configuration numerical Hartree‐Fock density. It is found empirically that in a given atom the shell boundaries are expressed as the successively increasing maxima in V(r)/ ρ(r) and the outermost maximum presents good approximate estimates of the core‐valence separation in atoms. The likeness in behavior of V(r)/ ρ(r) at each shell boundary with the maximum hardness principle is discussed. The single‐exponent‐fit parameters for the electron density in the valency region are provided for all atoms. © 1995 John Wiley & Sons, Inc.
The implementation of analytical energy gradients based on a quasi‐relativistic density functional method: The application to metal carbonyls
Authors: Schreckenbach Georg , Ziegler Tom , Li Jian 
Published: December 2004

AbstractThe capabilities of the quasi‐relativistic scheme due to J. G. Snijders at al. [Mol. Phys, 38, 1969 (1979) Ibid., J. Phys. Chem. 93, 3050 (1989)] has been extended by deriving expressions for the energy gradients with respect to the total energy EQR and implementing them into the ADF program system [B. to Velde and E. J. Baerends, Int. J. Quantum Chem. 33, 87 (1988)]. This implementation enables automated geometry optimization at the relativistic level. The new scheme has been applied together with a self‐consistent nonlocal density functional scheme, NL–SCF + QR, to the calculation of MCO bond lengths and the first bond dissociation energy (FBDE) in the binary transition metal carbonyls M(CO)5 (M = Fe, Ru, Os) and M(CO)6 (M = Cr, Mo, W). The calculated MCO bond lengths are in good agreement with available experimental data with an error typically smaller than 0.01 Å. The calculated FBDES are 45.7 (Fe), 33.0 (Ru), 34.7 (Os), 46.2 (Cr), 39.7 (Mo), and 43.7 (W) kcal/mol, respectively. These values compare well with the available experimental estimates of 42 (Fe), 28 (Ru), 31 (Os), 37 (Cr), 41 (Mo), and 46 (W), respectively. The relativistic effects are found to contract MCO bonds by between 0.07 and 0.16 A and strengthen the FBDEs by 5‐11 kcal/mol for third‐row compounds. The relativistic stabilization of the FBDES among the 5d elements makes, in general, the MCO bond of the 4d element weakest within a triad. © 1995 John Wiley & Sons, Inc.
Quantitative correlation of XPS linewidth with dislocation density in shock‐loaded ammonium perchlorate
Authors: Beard B. C. , Sandusky H. W. , Glancy B. C. , Elban W. L. 
Published: December 2004

AbstractThe linewidths of x‐ray photoelectron spectra have been correlated with dislocation densities in a shock‐damaged crystal of ammonium perchlorate (AP). A centimeter‐size AP crystal was non‐uniformly damaged by a rapidly decaying shock (peak pressure of 24.4 kbar at the entry surface), recovered intact and cleaved. The cleaved planes permitted interior analysis of the crystal by x‐ray photoelectron spectroscopy (XPS) over a pattern of 1 mm × 1 mm areas. The linewidth of the Cl 2p3/2 peak ranged from 1.70 eV for the region of greatest damage to 1.22 eV for the region demonstrating no visible damage, the same linewidth as that for unshocked AP (control). The correlation between dislocation density and XPS linewidth was quantitatively established by chemically etching and counting dislocations on cleaved planes from the shocked crystal. By this technique, a 100 × increase in dislocation density was determined for the region of greatest shock damage relative to undamaged crystal. Molecular orbital energy variation caused by distortion of the lattice in the vicinity of a dislocation is the physical mechanism responsible for the broadening of the photoelectron lines. Ab initio calculations of the Cl 2p energy level from various distorted perchlorate anion geometries have predicted orbital energy shifts sufficient to produce the observed linewidth broadening.
XPS reference procedure for the accurate intensity calibration of electron spectrometers— results of a BCR intercomparison co‐sponsored by the VAMAS SCA TWA
Authors: Seah M. P. 
Published: December 2004

AbstractA calibration procedure has been developed for XPS instrument intensity scales. The calibration is achieved by measuring the spectrum for reference foils of Ag, Au and Cu for which the true spectrum has been measured usng the metrology spectrometer. The ratio of the measured and reference spectra at 1 eV intervals from 200 eV kinetic energy to 1600 eV provides the calibration known as Q(E). The calibrations from all reference foils for a given instrument and setting should be the same and may be averaged to enhance accuracy. An interlaboratory study involving 58 different instruments, covering 25 different models from 9 manufacturers, has been completed with over 1200 individual spectra measured. The results show that the calibrations are excellent but that care is required or systematic errors may arise from instrumental problems such as x‐ray anode contamination, sample contamination, contributions from the sample holder and internal scattering in the spectrometer. However, these problems may be readily diagnosed. The Cu data often show carbon contamination and so those data are omitted from the assessments of Q(E).The instruments provide unmonochromated x‐rays from Al and Mg anodes as well as monochromated Al sources. The Q(E) curves for the unmonochromated sources always agree with each other whereas that for the monochromated source may agree with those for the unmonochromated sources in some instruments but not in others. The reason for the differences may lie in stray magnetic fields or lens magnification effects. The different reference materials give the same Q(E) on any given instrument for a given set of operating conditions with a typical scatter of 3% but actually ranging from 0.99% in the best case to 19.49% where problems, as noted above, occurred. Changing the slits or pass energy can change the relative intensities at low and high energy by more than a factor of 2. However, even larger differences may occur between instruments of the same model operated under identical settings in different laboratories. It is thus shown that each individual instrument needs a separate and regular calibration and that such a procedure would reduce the present intensity variations of a factor of 7 over the energy range 200–1400 eV to an average scatter of 3% or less.The individual calibrations for Q(E) for all of the 58 instruments are presented and it is shown that the methodology and reference data work effectively and consistently in all known situations where the reference procedure is adequately conducted.
Surface analytical study of the cause of mass gain of the kilogram prototype
Authors: Hashiguchi Y. , Mizuno K. , Nagoshi M. , Kasamura H. , Shiozawa K. , Fujita D. , Yoshihara K. 
Published: December 2004

AbstractThe International Prototype of the Kilogram, which is the only artificial material defining one of the fundamental constants, has been reported to gain mass as time elapses after it is cleaned. The surface of a Pt‐Ir alloy that has been used for the newer Kilogram prototypes was analysed by XPS and thermal desorption spectroscopy (TDS) to investigate the cause of mass gain, its time dependence and the effect of the cleaning method. The main cause of the mass gain was found to be adsorption of carbon (in the form of hydrocarbons) and oxygen (as water) from the atmosphere. The amounts of the two contaminant elements were almost saturated 6 months after sample cleaning. Cleaning methods do not make a large difference to adsorption behaviour. Although surface iridium is slightly oxidized, this effect is negligibly small.
Quantification of oxygen and carbon in high Tc superconducting films by (α,α) elastic resonance technique
Authors: Vizkelethy G. , Revsez P. , Mayer J. W. , Li Jian 
Published: December 2004

AbstractThe quantification of oxygen and carbon in high‐temperature (Tc) superconducting oxide thin films was made by employing elastic resonance in He backscattering analysis. A method combining the oxygen resonance technique and channeling was presented for measuring the nature of the oxygen disorder near the surface and the interface in a YBCO superconducting film grown on an MgO substrate. The oxygen resonance technique was used to quantify the oxygen profiling in the metal/YBCO contacts, showing that Zr and Nb act as sinks to oxygen from YBCO films and are oxidized in the forms Zr/ZrO2/YBCO/MgO and Nb0.2/YBCO/MgO after annealing in a vacuum at 350°C. We combined the carbon and oxygen resonances to determine the carbon contamination and oxygen concentration changes on the YBCO surface after coating and baking the photoresist. Residual carbon on the surface and a thin layer of oxygen depletion near the YBCO surface have been observed. The residual carbon in Bi2Sr2CaCu2O8 films made by the decomposition of metallo‐organic precursors was quantified using carbon resonance.
Universal energy dependence of the inelastic mean free path
Authors: Jablonski A. 
Published: December 2004

AbstractThe accuracy of quantitative XPS analyses using relative sensitivity factors is increased if matrix effects are accounted for in calculations of surface composition. This requires knowledge of the energy dependence of the inelastic mean free path (IMFP) for a given sample. It is sufficient for routine analyses to use the IMFP energy dependence averaged over a number of solids. A universal energy dependence is found to be better expressed by the Bethe equation than an equation of the form λ = aEp, although in both cases the energy dependence is controlled by one parameter. Values for these parameters are shown to depend on the class of solid: elements, inorganic compounds and organic compounds. The deviations of the assumed universal IMFP energy dependence from the true IMFP energy dependences for different solids is largest, exceeding 20%, in the energy range 200–500 eV. This deviation decreases to 3% at energies 500–1500 eV. Photoelectrons with kinetic energies within the latter energy range are recommended for quantitative XPS analysis using calculated sensitivity factors.
XPS study of the a‐C : H/Al2O3 interface
Authors: Ernst K.‐H. , Patscheider J. , Hauert R. , Tobler M. 
Published: December 2004

AbstractThe interface between diamond‐like amorphous hydrogenated carbon (a‐C : H) and Al2O3 was analysed by sputter depth profile analysis via x‐ray photoelectron spectroscopy. X‐ray photoelectron spectra were also recorded during direct ion beam deposition (CH4, E = 400 eV) monitoring the initial build‐up of the interface. No stoichiometric interface compound was detected, although Al2O3 is reduced to Al2O3‐x (x ∼ 0.5–1) enabling an interaction with the carbon atoms. This results in an excellent adhesion of a‐C : H to the chemically inert Al2O3.
X‐ray photoelectron spectroscopic study of ion etching and electrical biasing of silicon nitride on a carbon fiber
Authors: Rooke Michael A. , Sherwood Peter M. A. 
Published: December 2004

AbstractCarbon fibers with a chemical vapor‐deposited silicon nitride surface film have been investigated with core and valence band x‐ray photoelectron spectroscopy (XPS). The ability of the films to protect the fibers from oxidation was evaluated by heating, by argon and oxygen ion etching and by using an electrical biasing potential. Oxygen ion etching appears to oxidize the Si3N4 to SiO2, whereas argon etching removes the oxide and any hydrocarbon surface layer. The valence band data for Si3N4, Si2N2O, and SiO2 are interpreted by multiple scattered wave Xα calculations. The films crack when an electrical potential is applied, and the cracking is reproducible and irreversible, occurring particularly with a negative potential bias. We find chemical shifts on the core levels consistent with differential charging of the silicon nitride coating, an observation that is supported by sample biasing experiments. The work suggests that the cracking of the silicon nitride coating will significantly limit its effectiveness in protecting carbon fibers and carbon–carbon composites from oxidation.
Effect of metal stearate stabilizers on the thermal degradation of PVC in solution: The reversible blocking mechanism of stabilization
Authors: Iván Béla , Turcsányi Béla , Kelen Tibor , Tüdös Ferenc 
Published: December 2004

AbstractSystematic thermal degradation studies of PVC solutions have been carried out in the presence of different metal carboxylates (Pb‐, Cd‐, Ba‐, Ca‐ and Zn‐ stearates). ZnSt2 markedly accelerates degradation of the polymer. Significant induction periods (ti) for the appearance of free HCI are obtained in the presence of the other salts. CaSt2 acts mainly as an HCI‐scavenger and has no direct influence on the elimination process. Mainly short polyenes are formed during the induction period when PbSt2, CdSt2, and BaSt2 are used. After consumption of stabilizers rapid HCI loss occurs, and suddenly longer polyenes are formed, i.e., the amount of double bonds and the average length of polyenes sharply increases. At the same time, the rate of initiation (i.e., the rate of the polyene sequence formation) does not change at all around ti. None of the investigated stabilizers retard effectively the random initiation of HCI loss. In the presence of PbSt2, BaSt2, and CaSt2, and CaSt2, the initiation rate is nearly identical to that of the unstabilized PVC. The concentration of labile sites (h0) in PVC at the end of the induction period has been estimated by kinetic analysis. It has been found that in some cases h0 is higher than the concentration of labile structures in the virgin PVC. These results indicate that the main role of metal soap stabilizers is the blocking of the fast zip‐elimination of HCI from the PVC chain. It is likely that blocking occurs by attachment of a carboxylate group at the end of a propagating zip. This is a reversible process: the blocked structures become active again mainly after the consumption of stabilizers presumably by HCI‐catalyzed hydrolysis. In contrast to other stabilization mechanisms by Frye and Horst, Minsker and coworkers, and Michell the reversible blocking mechanism of PVC stabilization is able to explain the experimental findings presented in this study. It also explains such facts of practical importance as color stability of the resin during the induction period and fast blackening after the consumption of stabilizers.
Use of X‐ray fluorescence for sorting vinyl from other packaging materials in municipal solid waste
Authors: Summers James W. , Mikofalvy Bela K. , Little Scott 
Published: December 2004

AbstractX‐ray fluorescence of the chlorine atom is a suitable method for identifying vinyl in a mixed plastics stream in municipal solid waste. The chlorine X‐ray is weak and does not penetrate paper labels. There is also a rapid decrease in measured chlorine X‐ray intensity as the sample is moved away from the X‐ray source and detector which could be a potential problem for bottles of uneven shape.
Effect of an acrylic modifier on the brittle to ductile transition in poly(vinyl chloride)
Authors: Havriliak S. , Hemenway C. P. , Beswick G. T. 
Published: December 2004

AbstractInstrumented notched Izod measurements were made on test specimens cut from milled compression molded plaques of modified and unmodified poly(vinyl chloride) (PVC). The experimental variables were notch radius (from 0.025 to 6.35 mm in 8 steps) and two temperatures (23 and 12.5°C). Load‐time and energy‐time curves were determined under each set of experimental conditions, and each condition was replicated five times. The brittle to ductile transition is readily observed in this experimental range. The transition always occurs at shorter notch radii at each temperature for the modified PVC. In the transition region, the total energy drops from the 1,000 to 2,000 J/m range to less than 150 J/m. In this region, maximum loads remain the same while the times to break becomes much shorter for the brittle materials. These results suggest that the underlying molecular mechanism for brittle failure is the inability of the system to respond to the applied deformation. The oscillations observed in the printed output of the instrumented impact test were identified as having instrument rather than test specimen origins.
Mixed metal vinyl stabilizer synergism. III: Reactions of mixed metals and phosphites with a model compound
Authors: Grossman Richard F. 
Published: December 2004

AbstractIn the absence of mixed metal carboxylates, triaryl phosphites react rapidly with a model allylic compound for degrading vinyl, cinnamyl chloride, to yield phosphonium salts. On heating, these appear to yield allylidene phosphoranes by 1,1 elimination of HCl, with subsequent rearrangement to diphenyl phosphonates. With aryl alkyl phosphites, the phosphonium chloride intermediate undergoes rapid Arbusov rearrangement to the diphenyl phosphonate, eliminating alkyl chloride (or corresponding olefin). In the presence of zinc or cadmium carboxylates, Arbusov rearrangement is intercepted and chloride is transferred instead to the metal, forming the alkyl ester. The observed reaction paths appear to yield insight into the question of which phosphites are optimum for particular metal carboxylate blends and ratios in vinyl stabilizers, and into the related topic of which types of other additives are inappropriate.
Die design for rigid PVC—the effect of die land length on extrudate swell
Authors: Rabinovitch Elvira B. , Summers James W. , Booth Patrick C. 
Published: December 2004

AbstractPVC profile extrusion compounds have a unique morphology. While other polymers gradually decrease in extrusion die swell with increasing length/thickness (L/D) ratio, PVC profile extrusion compounds have a low die swell, quite independent of the die's L/D ratio in the range of 5 to 20. The fact that the die land length can be changed without changing the extrudate swell is an important consideration, which makes die design and balancing dies simpler and easier for PVC profile extrusion compounds. While other polymers substantially increase extrudate swell with increased shear rate, the swell of the PVC profile compounds is not much affected by shear or extrusion rate. This unique behavior allows wider processing latitude in profile extrusion and faster extrusion rates than with other polymers. Another unique factor in the rheology of PVC profile extrusion compounds is that extrusion die swell increases with increasing melt temperature, while other polymers have decreasing die swell with increasing melt temperature. The unusual rheology of PVC profile extrusion compounds is attributed to its unique melt morphology, where the melt flow units are 1 um bundles and molecules that have low surface to surface interaction and entanglement at low processing temperatures but increased melting and increased entanglement at higher processing temperatures. Other polymers, unlike PVC, have melt flow at the molecular level.