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[en] The presence of mixed valency in unconventional superconductors is a necessary consequence of the fact that there is chemical equilibrium between the atoms of a transition element having different oxidation states. Consequently, phases described by stoichiometric formulas such as FeSe, Ba(FeAs)2, La2CuO4 etc. deviate in fact from their nominal compositions. These deviations can be considered as doping by replacing some of the cationic atoms FeII and CuII in the conducting units by small amounts of Fe and Cu in higher, sometimes in lower oxidation state. From a consideration of the electronegativity values of the constituents of a selection of widely different unconventional superconductors and corresponding parent-compounds, it is evident that bonds between atoms of the conducting units have higher covalency than bonds between conducting units and charge reservoirs which are mixed ionic/covalent, and bonds within the charge reservoirs which are strongly ionic. In compounds without charge reservoirs, the bonds between neighbouring conducting units have van der Waals character. (orig.)
[en] Ab initio calculations of hydrogen bridge energies (EHB) of 2-halophenols were carried out at various levels of sophistication using a variety of basis sets in order to verify their ability in reproducing the experimentally-determined gas phase ordering, and the related experimental frequencies of the O-H vibration stretching mode. The semiempirical AM1 and PM3 approaches were adopted, too. Calculations were extended to the O-H...X bridge of a particular conformation of 2,4-dihalo-malonaldehyde. The results and their trend with respect to the electronegativity of the halogen series are highly dependant on the basis set. The less sophisticated 3-21G, CEP121G and LANL2DZ basis sets (with and without correlation energy inclusion) predict EHB decreasing on decreasing the electronegativity power whilst the opposite is generally found when more extended bases are used. However, all high level calculations confirm the nearly negligible energy differences between the examined O-H...X bridges
[en] A set of 146 well-established ionization potentials and electron affinities is presented. This set, referred to as the G2 ion test set, includes the 63 atoms and molecules whose ionization potentials and electron affinities were used to test Gaussian-2 (G2) theory [J. Chem. Phys. 94, 7221 (1991)] and 83 new atoms and molecules. It is hoped that this new test set combined with the recently published test set of enthalpies of neutral molecules [J. Chem. Phys. 106, 1063 (1997)] will provide a means for assessing and improving theoretical models. From an assessment of G2 and density functional theories on this test set, it is found that G2 theory is the most reliable method. It has an average absolute deviation of 0.06 eV for both ionization potentials and electron affinities. The two modified versions of G2 theory, G2(MP2,SVP) and G2(MP2) theory, have average absolute deviations of 0.08 endash 0.09 eV for both ionization potentials and electron affinities. The hybrid B3LYP density functional method has the smallest average absolute deviation (0.18 eV) of the seven density functional methods tested for ionization potentials. The largest deviation for the density functional methods is for the ionization potential of CN (>1thinspeV). The BLYP density functional method has the smallest average absolute deviation (0.11 eV) of the seven density functional methods tested for electron affinities, while the BPW91, B3LYP, and B3PW91 methods also do quite well. copyright 1998 American Institute of Physics
[en] On the basis of the viewpoint of structure-property relationship in solid state matters, we proposed some useful relations to quantitatively calculate the electronic polarizabilities of binary and ternary chalcopyrite semiconductors, by using electronegativity and principal quantum number. The calculated electronic polarizabilities are in good agreement with reported values in the literature. Both electronegativity and principal quantum number can effectively reflect the detailed chemical bonding behaviors of constituent atoms in these semiconductors, which determines the magnitude of their electronic polarizabilities. The present work provides a useful guide to compositionally design novel semiconductor materials, and further explore advanced electro-optic devices.
[en] Using a first principles approach to electron transport, we calculate the electrical and thermoelectrical transport properties of a series of molecular wires containing benzo-difuran subunits. We demonstrate that the side groups introduce Fano resonances, the energy of which is changing with the electronegativity of selected atoms in it. We also study the relative effect of single, double, or triple bonds along the molecular backbone and find that single bonds yield the highest thermopower, approximately 22 μV/K at room temperature, which is comparable with the highest measured values for single-molecule thermopower reported to date
[en] The interatomic distances in the transition states of radical hydrogen atom abstraction reactions X.+HY → XH+Y. determined by quantum chemical calculations are systematized and generalized. It is shown that depending on the reaction centre structure, these reactions can be subdivided into classes with the same X...Y interatomic distance in each class. The transition state geometries found by the methods of intersecting parabolas and intersecting Morse curves are also presented. The X...H...Y fragments are almost linear, the hydrogen atom position being determined by the reaction enthalpy. The effects of triplet repulsion, electronegativities and radii of X and Y atoms, the presence of adjoining π-bonds, and steric effects on the X...Y interatomic distances are analyzed and characterized. The bibliography includes 62 references.
[en] A systematic account is given of the current ideas about atomic and group electronegativities and the trends in the development of the concept of electronegativity are analysed. Attention is concentrated on the latest approaches to the definition of electronegativity - the concept of 'orbital' electronegativities and the density functional theory. A procedure is proposed for the determination of 'inductive' electronegativities, which permits a correct theoretical calculation of the electronegativity of a substituent from the electronegativities of individual atoms and the steric structure. It is shown that the approach developed has a series of important advantages - for example, it makes it possible to calculate the group electronegativities of isomeric substituents avoiding the principle of the equalisation of electronegativities. A survey of literature data and generalisation of the method proposed by the authors have made it possible to formulate the concept of electronegativity as an unchanging fundamental immanent characteristic of a chemical element. The bibliography includes 222 references.
[en] A first step towards understanding a complex plasma is usually to develop a zero-dimensional or global model. This is difficult when the plasma is electronegative, because the literature contains many proposed models with different and sometimes contradictory detailed assumptions, and different domains of applicability. The appropriateness of such models in a given context is often hard to assess. In this paper, we present a set of detailed kinetic simulations spanning a wide of range of parameters, especially with respect to electronegativity, collisionality and dominant negative ion destruction mechanism. We use these simulations as a benchmark to investigate the validity of the fundamental global model assumptions when used to model electronegative discharges. We reach two important conclusions: (1) that an accurate electron kinetics model is more important than detailed considerations relating to plasma dynamics in the presence of negative ions and (2) that there exists a simple and robust transport model that is in reasonable agreement with all of our benchmark simulations, when the electrons are treated properly.
[en] A suitable relationship between free-cation polarizability and electronegativity of elements in different valence states and with the most common coordination numbers has been searched on the basis of the similarity in physical nature of both quantities. In general, the cation polarizability increases with decreasing element electronegativity. A systematic periodic change in the polarizability against the electronegativity has been observed in the isoelectronic series. It has been found that generally the optical basicity increases and the single bond strength of simple oxides decreases with decreasing the electronegativity. The observed trends have been discussed on the basis of electron donation ability of the oxide ions and type of chemical bonding in simple oxides. - Graphical abstract: This figure shows the single bond strength of simple oxides as a function of element electronegativity. A remarkable correlation exists between these independently obtained quantities. High values of electronegativity correspond to high values of single bond strength and vice versa. It is obvious that the observed trend in this figure is closely related to the type of chemical bonding in corresponding oxide. Highlights: ► A suitable relationship between free-cation polarizability and electronegativity of elements was searched. ► The cation polarizability increases with decreasing element electronegativity. ► The single bond strength of simple oxides decreases with decreasing the electronegativity. ► The observed trends were discussed on the basis of type of chemical bonding in simple oxides.