A molecular electrostatic potential bond critical point model for atomic and group electronegativities

A consistent set of atomic electronegativities of main block and d-block transition elements has been obtained from the position and value of the molecular electrostatic potential bond critical point of the C-E bond of a methyl-element-hydride system, H(3)C-EH(n) (E is an element and n = 0, 1, 2, 3, 4, and 5 depending on the position of E in the periodic table). The new scale shows very good agreement with the popular electronegativity scales such as Pauling, Allen, Allred-Rochow, Mulliken, and Sanderson scales of electronegativity, especially for the main block elements. The present scale of electronegativity for transition elements is expected to be more accurate than the previously derived values because of a more consistent approach. Further, the same approach has led to the evaluation of group electronegativities when the hydrogens of E are replaced by other substituent groups. These group electronegativity values are found to correlate well with Inamoto and Mullay scales.     

Improved local density functional approach for atomic systems

Through a new local density approximation to the kinetic energy density functional introduced by us recently, a simple Thomas–Fermi-like scheme for the direct calculation of electron density in atoms is proposed. The calculated density is nonsingular at the nucleus and the energy values are in very good agreement with the corresponding Hartree–Fock results for atoms. © 1994 John Wiley & Sons, Inc.     

The correlation potential for two-electron atomic ions

The correlation potential is computed for two electron atomic ions with atomic numbers from 1 to 10 using the charge density reconstructed from a natural orbital expansion of a Kinoshita-like atomic wave function. Over the wide range of densities involved, the correlation potentials are not even approximately a local function of the density.     

Improved upper bounds for the atomic ionization potential

Two sets of rigorous upper bounds on the atomic ionization potential are derived from some known inequalities of the classical analysis. The first set of bounds are expressed in terms of radial expectation values of the electron density; they improve previously found bounds of the same kind and converge to the exact ionization potential. The other bounds depend on various atomic density functionals which describe global physical quantities such as the Thomas–Fermi and exchange energies and the Boltzmann–Shannon information entropy. The accuracy of some of the bounds is numerically analyzed within a Hartree–Fock framework. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 71: 185–189, 1999     

An analytic model for atomic clusters

The paper presents an analytic model which is based on approximation of the catchment basins in cluster potential energy surface by structures of ash-tray type. In order to see how the quantities to be specified relate to those obtained by means of numerical computation, predictions for the Ar₁₃ caloric curve are made and they are compared with computer simulation data.     

First-principles calculation of local atomic polarizabilities

Common methods of determining atomic polarizabilities suffer from the inclusion of nonlocal effects such as charge polarization. A new method is described for determining fully ab initio atomic polarizabilities based on calculating the response of atomic multipoles to the local electrostatic potential. The localized atomic polarizabilities are then used to calculate induction energies that are compared to ab initio induction energies to test their usefulness in practical applications. These polarizabilities are shown to be an improvement over the corresponding molecular polarizabilities, in terms of both absolute accuracy and the convergence of the multipolar induction series. The transferability of localized polarizabilities for the alkane series is also discussed.     

Determination of barium in strongly mineralised waters by atomic absorption spectrometry

Sulphur trioxide is directly titrated in fuming sulphuric acid (oleum) with water in the form of diluted sulphuric acid. A nickel electrode is used and a newly developed mercury/mercuric(I)-sulphate reference electrode. The heat of hydration must be hold under control by means of an ice bath and by variation of the speed of titration.     

The rapid determination of barium in bone by atomic absorption spectrophotometry

A rapid and precise method for the determination of barium in bone is presented. Barium as the nitrate is directly separated from calcium by co-precipitation with added strontium using fuming nitric acid. Atomic absorption measurements are made at 553.6 nm using a nitrous oxide-acetylene flame in the presence of strontium and potassium, and being free from noise due to the emission of CaOH. In order to improve accuracy and speed a radioactive tracer is used.     

Role of local structure on motions on the potential energy landscape for a model supercooled polymer

We have conducted detailed Monte Carlo and molecular dynamics simulations of a model glass forming polymeric system near its apparent glass transition temperature. We have characterized the local structure of the glass using a Voronoi-Delaunay analysis of local particle arrangements. After a perturbative face elimination, we find that a significant fraction of Voronoi polyhedra consist of 12 pentagonal faces, a sign of icosahedral ordering. Further, we have identified metabasins of particle vibrations on the potential energy landscape on the basis of persistence of particle positions and neighbors over a simulated trajectory. We find that the residence times for vibrations are correlated with a particular Voronoi volume and number of neighbors of a particle; the largest metabasins correspond to particles whose average Voronoi volume is close to the value expected on the basis of the density, and whose approximate number of neighbors is close to 12. The local distortion around a particle, measured in terms of the tetrahedricity of the Delaunay simplices, reveals that the particles with a higher degree of local distortion are likely to transition faster to a neighboring metabasin. In addition to the transition between metabasins, we have also examined the influence of vibrations at inherent structures (IS) on the local structure, and find that the the low frequency modes at the IS exhibit the greatest curvature with respect to the local structure. We believe that these results establish an important connection between the local structure of glass formers and the activated dynamics, thereby providing insights into the origins of dynamic heterogeneities.     

A new method for the calculation of atomic and local hardness

The relationships between atomic hardness, atomic electronegativity, and electronic energy are considered and emphasized. A new method for calculating atomic hardness is described. The concept of local hardness is quantified through the calculation of a new variable named alfahardness. Atomic hardness and alfahardness are used for the calculation of both the mean molecular and local properties. The results obtained are discussed and a comparison made with the analogous quantities presented by Pearson. An algorithm has been realized and transformed into a computer routine for use within a CAOS program.     

Determination of calcium and barium in steel by electrothermal atomic emission spectrometry

A simple and rapid method is described for the determination of 1–40 μg g^?1 calcium in steels by electrothermal atomic emission spectrometry. The sample is dissolved in nitric acid and does not need preconcentration. The use of a recessed platform is shown to improve reproducibility and sensitivity in the determination of calcium. A similar procedure for the determination of barium (< 1 μg g^?1 in steel is described.     

石墨炉原子吸收光谱法测定食盐中钡

建立了石墨炉原子吸收光谱法测定食盐中钡的方法,不需要对石墨管做任何处理,也无需对样品进行除盐处理,通过优化石墨炉升温程序,极大改善了食盐样品中钡测定的灵敏度和峰型。钡在0.00~50.0 μg/L浓度范围呈现良好的线性关系,相关系数优于0.999,检出限为0.650 mg/kg(以称样量0.200 g,定容至50 mL计算)。食盐样品钡加标回收率范围为81.3%~105.1%,相对标准偏差在8.9%以内。方法稳定可靠,准确度较高,适用于食盐中钡的测定。     

The self-interaction correction to the local spin density model: Effect on atomic momentum space properties

Perdew and Zunger showed that the exact energy density functional for the ground state is strictly self-interaction-free. However, the local spin density (LSD) approximation lacks this self-interaction correction (SIC). Perdew and Zunger studied the effect on coordinate-space properties of incorporating the SIC. In the present study we examine the effect of SIC on momentum space properties, viz. the electron momentum distribution, ⊂p″⊃ values, electron momentum densities and the Compton profiles for atoms He to Ar. A remarkable improvement is seen in all the momentum space properties of the SIC LSD model over the LSD model when compared to their near Hartree-Fock counterparts.     

A kinetic model for an atomic absorption signal

A kinetic model is proposed for describing the shape of an atomic absorption signal in the case of first-order kinetics. The formation energy of free copper ions (87 x 7 kJ/mol) and other kinetic parameters of an atomic absorption signal of copper at 2273–3073 K were determined from the experimental data.     

Indirect automatic atomic absorption determination of sulphate based on its precipitation with barium

A continuous precipitation flame atomization atomic absorption spectrometric method for the indirect determination of sulphate is proposed. By using a reversed flow-injection configuration for precipitation as barium sulphate, this anion was determined in the range 10–150 g/ml, with a relative standard deviation of 2.6%. The sensitivity was increased by a factor of seven by using a nitrous oxide-acetylene flame to measure barium.     

Step structure in the atomic Kohn-Sham potential

In this work we analyze the exchange-correlation potentialv _xc within the Kohn-Sham approach to density functional theory for the case of atomic systems. The exchange-correlation potential is written as the sum of two potentials. One of these potentialsv _xc,scr is the long-range. Coulombic potential of the coupling constant integrated exchange-correlation hole which represents the screening of the two-particle interactions due to exchange-correlation effects. The other potentialv _xc,scr ^resp contains the functional derivative with respect to the electron density of the coupling constant integrated pair-correlation function representing the sensitivity of this exchange-correlation screening to density variations. As explicit expression of the exchange-part of this functional derivative is derived using an approximation for the Greens function of the Kohn-Sham system and is shown to display a distinct atomic shell structure. The corresponding potentialv _xc,scr ^resp has a clear step structure and is constant within the atomic shells and changes rapidly at the atomic shell boundaries. Numerical examples are presented for the Be and Kr atoms using the Optimized Potential Model (OPM).     

Molecular similarity based on atomic electrostatic potential

We propose a new similarity measure operating in the space spanned by the potential values, evaluated at atoms constituting the benzene ring and the COOH group in para-substituted benzoic acids and at benzene ring atoms in monosubstituted benzenes. The similarity measures are equivalent to the Euclidean distance between points in that space. Only the distances between the potentials at corresponding atoms in different molecules are included. The distances for benzene rings were very similar, regardless of whether they were calculated in para-substituted acids or in monosubstituted benzenes. As reference reactions, dissociation of benzoic acids and nitration of monosubstituted benzenes have been used. The effects of reduction of dimensionality of the potential space on the comparison of similarity measures with the free energies of the reference reactions have been investigated. It became obvious that the potentials at individual atoms in molecules of the acids and monosubstituted benzenes are mutually correlated to a high degree.     

Synthesis and characterisation of cyclopentadienyl complexes of barium: precursors for atomic layer deposition of BaTiO3

Cyclopentadienyl complexes Ba(C5Me5)2(THF)2 (1), Ba(C5Me5)2(A) (A = THF, dien, trien, diglyme, triglyme) (2-5), Ba(Pr(i)3C5H2)2(THF)2 (6), Ba(Bu(t)3C5H2)2(THF) (7), Ba(Me2NC2H4C5Me4)2 (8) and Ba(EtOC2H4C5Me4)2 (9) were prepared and characterised with TGA/SDTA, NMR and MS. Crystal structures of 2, 4, 5, 7, 8 and 9 are presented. All complexes prepared sublime under reduced pressure and complexes 1, 6 and 7 showed volatility also under atmospheric pressure. Complexes 1, 6 and 7 lose the coordinated THF when evaporated while complexes 2-5 are sublimable as complete molecules under reduced pressure. Complexes with bulky cyclopentadienyl ligands (6 and 7) are the most thermally stable and volatile among the prepared barocenes. X-ray structure determinations reveal that all the complexes studied are monomeric. Complexes 1, 7 and 8 were successfully tested in BaTiO3 thin film depositions by atomic layer deposition (ALD).