Role of electronegativity in the qualitative inference of the TOF–SIMS fragment pattern of inorganic compounds

The role of the electronegativity of atoms in inorganic compounds in TOF–SIMS fragmentation is discussed. From a study of approximately 30 inorganic compounds – chlorides, oxides, nitrates, and sulfates – a simple rule has been proposed for the dependence of fragment pattern appearance on the electronegativity (electron affinity), which can be easily obtained from handbooks, and the valence of positive and negative ions in these compounds. TOF–SIMS measurements of metal and alloy surfaces, should be corrected for the ionization potentials and/or electronegativities of atoms present in surface contaminants. Received: 9 October 2000 / Revised: 26 February 2001 / Accepted: 1 March 2001     

Molecular electronegativity in density functional theory (II) --Direct calculation of group electronegativity and the atomic charges in a group

On the basis of a more precise expression of the atomic effective electronegativity deduced from the density functional theory and electronegativity equalization principle, a new scheme for calculating the group electronegativity and the atomic charges in a group is proposed and programed, and various parameters of electronegativity and hardness are given for some common atoms. Through calculation, analysis and comparison of more than one hundred groups, it is shown that the results from this scheme are reasonable and may be extended.     

Electronegativities of elements in covalent crystals

A new electronegativity table of elements in covalent crystals with different bonding electrons and the most common coordination numbers is suggested on the basis of covalent potentials of atoms in crystals. For a given element, the electronegativity increases with increasing number of bonding electrons and decreases with increasing coordination number. Particularly, the ionicity of a covalent bond in different environments can be well-reflected by current electronegativity values; that is, the ionicity of chemical bonds increases as the coordination number of the bonded atoms increases. We show that this electronegativity scale can be successfully applied to predict the hardness of covalent and polar covalent crystals, which will be very useful for studying various chemical and physical properties of covalent materials.     

Prediction of proton magnetic resonance shifts: The dependence on hydrogen charges obtained by iterative partial equalization of orbital electronegativity

Proton chemical shifts correlate linearly with charges on hydrogen obtained by a method for iterative partial equalization of orbital electronegativity. The compounds studied comprise a wide variety of classes of molecules; all points fall on a single correlation line, showing the general importance of electronic effects in proton chemical shifts and the physical significance of the atomic charges. On the other hand, as there is no general correlation between charges on carbon and on hydrogen atoms, proton chemical shifts cannot be used as probes for charge densities on carbon atoms. Deviations from the correlation line can be attributed to anisotropy effects and provide an estimate for their magnitude.     

System of metal electronegativities calculated from the force constants of the bonds

It is proposed to use a unified one-parameter equation which relates the force constants in molecules and crystals to the electronegativities of atoms. The results obtained for all currently studied compounds depend little on the ligand type, which made it possible to construct a complete electronegativity scale for elements in molecular and crystalline states equivalent in known cases to the thermochemical Pauling scale. An attention is paid to the chemical bond characteristics in some molecules and crystals of b subgroups.     

Multipole moment analysis for hydrides,fluorides, and lithium compounds of first- and second-row elements

A method is presented that conserves all local dipole moments in a partitioning of overlap charge between pairs of atoms. The approximate conservation of quadrupole and higher-moment components can be used as a criterion for the suitability of atomic basis sets. Ab initio calculations are presented for hydrides, fluorides, and lithium compounds of first- and second-row elements in a systematic study of compounds and basis sets. The best suitable basis set for each series is determined by the criterion of best approximate conservation of quadrupole moment components. A linear relation between charge shifts and Mulliken electronegativity differences is established for diatomic molecules. © 1993 John Wiley & Sons, Inc.     

Rapid estimation of charge distribution. II. Heteroatoms

A rapid method for estimating CNDO charges in large data bases using a reparameterized Del Re method has been described previously. In this article the method is extended to saturated compounds containing B, N, O, F, Si, P, S, and Cl. Good results are obtained by forcing the Del Re δ^o parameter for each element to be linearly related to its Pauling electronegativity, but with the slopes and intercepts being different for second- and third-row elements. With a test set of 17 compounds and 71 atoms, the CNDO charge was reproduced with an average deviation of ±0.03. The largest deviations, up to ±0.2, were observed for carbons having multiple F or Cl substituents and for sterically hindered atoms. © 1992 by John Wiley & Sons, Inc.     

Chemometric evaluation of time-of-flight secondary ion mass spectrometry data of minerals in the frame of future in situ analyses of cometary material by COSIMA onboard ROSETTA

Chemometric data evaluation methods for time-of-flight secondary ion mass spectrometry (TOF-SIMS) have been tested for the characterization and classification of minerals. Potential applications of these methods include the expected data from cometary material to be measured by the COSIMA instrument onboard the ESA mission ROSETTA in the year 2014. Samples of the minerals serpentine, enstatite, olivine, and talc have been used as proxies for minerals existing in extraterrestrial matter. High mass resolution TOF-SIMS data allow the selection of peaks from inorganic ions relevant for minerals. Multivariate cluster analysis of peak intensity data by principal components analysis and the new method CORICO showed a good separation of the mineral classes. Classification by k nearest-neighbor classification (KNN) or binary decision trees (CART method) results in more than 90% correct class assignments in a leave-one-out cross validation.     

Electronegativity and hardness in the chemical approximation

The chemical electronegativity of an atom (Mulliken definition) has been identified with the average value of χ, the electronegativity function given by the rigorous density functional theory. An appropriate definition of hardness is developed, and a scale of hardness for bonded atoms is proposed. The electrodynamical atom model is demonstrated to produce a simple relation between atomic hardness and size. Electronegativity has been calculated for bonded atoms in a variety of molecules and crystals, covalent and ionic, without any specific approximation for the energy function E(q). Expressions for the electronegativity of a molecule have been derived and critically discussed.     

Significance of crystallochemical factors in chemical reactions into the structure of solids

The chemical reaction of the formation of compounds within the structure of solid as a reaction medium??internal reactions??is the subject of the article. The mechanism of these reactions on the example silicate mineral structure and nanocrystallization of oxide glasses is considered. Local atoms interaction analysis based on the electronegativity of and ionicity of the chemical bonds values helps to understand this mechanism and predict course of intrastructural thermal processes.     

Correlation of bond metallicity measures to electronegativity for binary oxides

We have investigated alkali, alkaline‐earth, and rutile binary oxides within density functional theory (DFT) and Bader's atoms‐in‐molecules theory, focusing on properties of bond and ring critical points, and their relations to band gap and Pauling electronegativity. We find linear relations of kinetic energy density, electron density, and the gap divided by kinetic energy density at the bond critical points to the difference of Pauling electronegativities of the cation and oxygen anion. At the ring critical points of rutile compounds, we also find that some bond metallicity measures are linearly related to the difference of electronegativities. This study extends our knowledge about the relations between bond critical points, band gap, and electronegativity, but also shows for the first time a quantitative relation between quantities at the ring critical points and global properties of the compounds.     

Electronegativity through the energy function

The modern idea of electronegativity based on the E(q) function and the traditional chemical electronegativity are brought together in one self-contained expression. The electronegativity of a molecule is confronted with the in situ electronegativities of the component atoms.     

A new scale of electronegativity based on electrophilicity index

By calculating the energies of neutral and different ionic forms (M2+, M+, M, M-, and M2-) of 32 elements (using B3LYP/6-311++G** level of theory) and taking energy (E) to be a Morse-like function of the number of electrons (N), the electrophilicity values (omega) are calculated for these atoms. The obtained electrophilicities show a good linearity with some commonly used electronegativity scales such as Pauling and Allred-Rochow. Using these electrophilicities, the ionicities of some diatomic molecules are calculated, which are in good agreement with the experimental data. Therefore, these electrophilicities are introduced as a new scale for atomic electronegativity, chi(omega)0. The same procedure is also performed for some simple polyatomic molecules. It is shown that the new scale successfully obeys Sanderson's electronegativity equalization principle and for those molecules which have the same number of atoms, the ratio of the change in electronegativity during the formation of a molecule from its elements to the molecular electronegativity (Delta chi/chi omega) is the same.     

TOF-SIMS and XPS-investigations of ion implanted single crystal 1b-diamonds

Near surface zones of (48)Ti- and (52)Cr-implanted single crystal diamonds (1b-MCD) were characterized by XPS, TOF-SIMS and white light interference microscopy (WLI). By the combination of WLI and TOF-SIMS it was possible to calibrate the depth scale of TOF-SIMS and XPS depth profiles quantitatively. The adjustment of TOF-SIMS and XPS elemental depth profiles in the implantation maximum increases the quantitative detection limit of the implanted elements by more than two orders of magnitude and enables the interpretation of results from wear simulation experiments. Peak fits of XPS C(1s)-photolines indicate the fraction and chemical nature of carbide-like structures in the implantation zone. Qualitative hints on carbide compounds are possibly included in the reconstructed TOF-SIMS spectra but this information can presently only be extracted with the aid of XPS analyses.     

A scheme for the economical use of numerical basis sets in calculations with SIESTA

We demonstrate the effectiveness of an economical scheme that uses numerical basis sets in computations with SIESTA. The economical basis sets demonstrated, in which high-level double-zeta basis plus polarization orbitals (DZP) are applied only for atoms of strong electronegativity and metal atoms while a double-zeta basis is applied to the rest of the atoms of small proton-bound carboxylic acid clusters and sodium–organic compounds, predict correct geometric structures very close to those obtained using DZP for all atoms. The use of economical basis sets can save about 30–50% of the CPU time that is used for calculations with large basis sets. This study provides a general guideline for basis set selection in SIESTA computations of large systems.Acknowledgement. The work described in this paper was fully supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China (project no. CityU 1033/00P).     

Modification of Wiener Index and its application

A novel topological index based on the Wiener Index is proposed as W* = 1/2 sigma (n)(i,j=1) S(*)(ij), the element S(*)(ij) of the distance matrix is defined either as S(*)(ij) = alpha x square root of I(i)I(j)/R(ij) (atoms i and j are adjacent) or as S(*)(ij) = = alpha x (j-i+1)square root of I(i) x x x x x I(j)/R(ij) (atoms i and j are not adjacent), where I(i) and I(j) represent the electronegativity of vertices i or j, respectively, R(ij)() is the sum of the bond length between the vertices i and j in a molecular graph, and alpha = (Z(i)/Z(j))(0.5), where Z(i) and Z(j) are the atomic numbers of the positive valence atom i and the negative valence atom j, respectively. The properties and the interaction of the vertices in a molecule are taken into account in this definition. That is why the application of the index W to heteroatom-containing and multiple bond organic systems and inorganic systems is possible. Correlation coefficients above 0.97 are achieved in the prediction of the retention index of gas chromatography of the hydrocarbons, the standard formation enthalpy of methyl halides, halogen-silicon, and inorganic compounds containing transition metals.