Calculated Charge Distributions Research Articles

Calculation of voltage and space charge distributions in a wire-plate electrostatic precipitator

Several convergence acceleration methods have been introduced into procedures developed by the Southern Research Institute for calculating voltage and space charge distributions in parallel plate electrostatic precipitators. A dominant eigenvalue method is used in conjunction with several other techniques to promote convergence of an iterative calculation of these quantities. In each of two test problems, the effect of the acceleration step was to reduce the required computation time to roughly 5% of its original value.

Electronegativity equalization and the electronic structure of polyhedral clusters of main‐group atoms

AbstractThe concept of the equalization of atomic electronegativities accompanving molecule formation is applied to a study of the electronic structure of polyhedral clusters of main‐group atoms such as Ge, Sn, Pb, Tl, and Bi. Emphasis is placed upon charged clusters such as Sn9−x Pb(x = 0 → 9), Sn9‐xGe, Sn8−xPbx Tl5−, Sn2Bi, SnTe, etc. The role of the relativistic spin‐orbit splitting of an np shell into np1/2 and np3/2 subshells in modifying atomic and hence molecular electronegativities is discussed. Correlations are made between calculated charge distributions and observed199 Sn NMR chemical shifts for clusters of a given size and charge. It is concluded that a useful picture of charge distributions in these clusters may be obtained from electronegativity equalization considerations.

ChemInform Abstract: MNDO STUDY OF THE PROTON AFFINITY OF FLUORINATED FORMALDEHYDES AND ACETONES

Abstract The MNDO molecular orbital method is employed to calculate the proton affinities of fluorinated formaldehydes and acetones. Agreement with experimentally reported proton affinities is good. In the acetone series a decrease in proton affinity is calculated for each successive fluorine substituent. The calculated strength of the intramolecular hydrogen bond in the protonated fluoro-formaldehydes and acetones is 0.6—2.7 kcal mol −1 , in good agreement with the experimental value of 2—3 kcal mol −1 in the protonated fluoroacetones. Examination of the calculated charge distribution shows that the trends in proton affinity can be understood qualitatively both in terms of initial-state and final-state effects caused by the fluorine substituents. Protonation at the fluorine atom is less stable by about 25 kcal mol −1 than protonation at the oxygen atom for monofluoroacetone.

MNDO study of the proton affinity of fluorinated formaldehydes and acetones

The MNDO molecular orbital method is employed to calculate the proton affinities of fluorinated formaldehydes and acetones. Agreement with experimentally reported proton affinities is good. In the acetone series a decrease in proton affinity is calculated for each successive fluorine substituent. The calculated strength of the intramolecular hydrogen bond in the protonated fluoro-formaldehydes and acetones is 0.6—2.7 kcal mol −1, in good agreement with the experimental value of 2—3 kcal mol −1 in the protonated fluoroacetones. Examination of the calculated charge distribution shows that the trends in proton affinity can be understood qualitatively both in terms of initial-state and final-state effects caused by the fluorine substituents. Protonation at the fluorine atom is less stable by about 25 kcal mol −1 than protonation at the oxygen atom for monofluoroacetone.

Electronic structure of CsAu

Self-consistent non-relativistic and relativistic LMTO band structure calculations have been carried out for CsAu. In the non-relativistic model CsAu is a metal, whereas — in agreement with experiments — the relativistic calculations predict CsAu to be a semiconductor. The gap is not caused by the spin-orbit coupling. The importance of the core-like Cs-5 s and Cs-5 p states for the alloy formation is discussed, and charge distribution calculations are used to illustrate the ionic nature of the bonding.

Acid-catalyzed hydrolysis of 2-methoxypropenal

2-Methoxypropenal in acid media undergoes general acid-catalyzed hydrolysis with formation of 2-oxopropanal. The kinetics of this reaction were studied, the rate constants established, and a reaction mechanism is suggested. Hydrolysis of 2-methoxypropenal is governed by a mechanism of the vinyl ether type, and the presence of the aldehyde group causes a decrease in the reaction rate. The analogy of the acid-catalyzed hydrolysis of 2-methoxypropenal to that of a vinyl ether was shown by the solvent isotope-effect, k D/ k H = 0.41, and the value of the Brönsted exponent, α = 0.60. The activation parameters found and quantum-chemical calculations of charge distribution in 2-methoxypropenal and other model compounds were also utilized to explain the mechanism of the acid-catalyzed hydrolysis of the title compound.

Quantumchemical interpretation of a typical fragmentation in the mass spectra of benzoquinolizine derivatives

The results of some quantumchemical calculations, performed by the use of the semi-empirical CND0/2 method, are compared with findings of the mass spectrometric investigations. The calculated charge distributions, force values and Wiberg indices, revealed useful informations on the properties and behaviour of the molecule in question and provided support for the suggested fragmentation pathway.

MNDO study of the proton affinity of fluorinated formaldehydes and acetones

The MNDO molecular orbital method is employed to calculate the proton affinities of fluorinated formaldehydes and acetones. Agreement with experimentally reported proton affinities is good. In the acetone series a decrease in proton affinity is calculated for each successive fluorine substituent. The calculated strength of the intramolecular hydrogen bond in the protonated fluoro-formaldehydes and acetones in 0.6–2.7 kcal mol −, in good agreement with the experimental value of 2–3 kcal mol − in the protonated fluoroacetones. Examination of the calculated charge distribution shows that the trends in proton affinity can be understood qualitatively both in terms of intial-state and final-state effects caused by the fluorine substituents. Protonation at the fluorine atom is less stable by about 25 kcal mol − than protonation at the oxygen atom for monofluoroacetone.

Charge Distribution among Graphite Layers in High-Stage Alkali-Graphite Intercalation Compounds

The charge distribution among graphite layers in graphite intercalation compounds, C 12 u M ( n ≥3, M=K, Rb, Cs) is calculated on the basis of a two-dimensional band structure for each layer. Electronic states in each layer are described within the framework of the tight-binding method taking into account the polarization of π orbitals of carbon atoms. It is shown that more than 90% of the excess electrons transferred from donor intercalants are localized on the bounding graphite layers. The stage dependences of electronic specific heat and resistivity of the compounds are discussed in relation to the calculated charge distribution.

Field effect in semiconductor critical-thickness layers

Theoretical electrostatic characteristics of structures based on metals, insulators, and semiconductor layers with thickness comparable to or less than the Debye screening radius (critical thickness layers) and semiconductors of semi-infinite geometry are studied. Some peculiarities of electric field screening in semiconducting critical-thickness layers are revealed on the basis of computer calculations of potential and charge distributions as well as differential capacitances as a function of applied voltage. The obtained characteristics are compared with characteristics of analogous semiconducting structures with semi-infinite geometry. [Russian Text Ignored]

π-Electron ring currents and magnetic properties of porphyrin molecules in the MO LCAO SCF method

The coupled variant of double-parameter perturbation theory in the MO LCAO SCF method in the London approximation has been used for the calculation of π-electron current distributions in the molecules of porphin and its derivatives. The chemical shifts of1H-NMR have been computed on the basis of calculations of ring currents and charge distributions. It is shown that π-electron ring currents are responsible for the dominant contribution to the shielding of protons. The theoretical and experimental values of proton chemical shifts are in a good agreement. Chemical shifts of the13C and15N nuclei have also been estimated. Two aromaticity scales are proposed for the compounds under study based on the calculations of the π-electron contribution to the diamagnetic susceptibility and of π-electron currents, respectively.

A method of numerical analysis and calculation of lonic space charge distribution and its polarization by a hopping model

A method of numerical analysis and calculation of lonic space charge distribution and its polarization by a hopping model

Structural Changes on Oxidation: Flattening of the C4‐Cluster of Tetrahedrane

As a cluster with a “balanced” number of electrons, tetra‐tert‐butyltetrahedrane surprisingly affords the same radical cation as tetra‐tert‐butylcyclobutadiene on electron removal. The spontaneous valence isomerization can be explained on the basis of the calculated charge distribution.

Ab initio studies on amides: conformational preferences of formimide and barriers to interconversion of the conformers

Formimide (diformamide), the parent of the diacylamines, is capable of existing in three basic ground-state conformations about the N-C bonds. Full geometry optimization with the STO-3G basis set predicts that all three conformers are fully coplanar, that the E,E (1) and E,Z(3) conformers are of similar energy, and that the Z,Z (2) conformer is of somewhat higher energy (by 11 kJ mol-1); 4-31G evaluation of the energies suggests that (2) is by far the least stable and that (1) is of higher energy than (3) by 6.5 kJ mol-1. Analysis of the calculated charge distribution suggests that (2) is destabilized by electrostatic repulsion. These results are consistent with experimental conclusions that planar (3) is strongly preferred in the vapour state at room temperature and that (2) has not been observed in the vapour state or in solution. Partial geometry optimization with the STO-3G basis set of model transition states for internal rotation suggests a barrier height of 52 kJ mol-1 (72 kJ mol-1 when evaluated with the 4-31G basis set) for the conversion (3) → (1).

Theoretical considerations on the oxidation of propylene on transition metal molybdates

Molecular orbital calculations of charge distributions for the π-allyl complex with transition metal ions in molybdates show that the activated π-allyl species is formed by transfer of charge density to the metal ion. The relative charge distributions on the three carbon atoms of the adsorbed allyl species govern the course of oxidation reaction.

Study of an electrically driven jet

This is a study of the charge distribution and the forces on an electrically driven jet. A numerical solution of the charge distribution is presented, based on the measurement of the jet profile and the jet current. The influence of the charge distribution and fluid conductivity on jet length is considered. As a check on the charge distribution calculations, the electric driving forces are compared to the reaction forces.

Micromagnetics of curling configurations in magnetically soft cylinders

The response of an ideally soft magnetic cylinder is calculated by approximating magnetostatic interactions while taking into account the exchange energy of curling patterns with point singularities. Detailed calculations of the magnetic surface charge distribution of paramagnetic materials are used as a guide in parameterizing an approximate charge distribution suitable for applying the Ritz method to the micromagnetic problem of ferromagnetic materials without anisotropy or magnetostriction. Numerical results are given for a cylinder with L/D=1 for fields below saturation illustrating how remanence and coercivity depend on the ratio of the exchange length A/M2o to sample dimensions. The role of point singularities in remanence, coercivity, nucleation and irreversibility is outlined.

Electric potential difference between conjugate points in middle latitudes caused by asymmetric dynamo in the ionosphere.

A new method is proposed for calculation of electric charge distribution in the ionosphere associated with the dynamo action for any given air motion. If the dynamo action is asymmetric in the northern and southern hemispheres, the electric potential difference of the order of 1kV will be produced (if the field-aligned current is prohibited) at the conjugate pair of stations in middle latitudes although the potential difference will be almost cancelled by the field-aligned currents in the magnetosphere flowing from the winter hemisphere to the summer hemisphere. It is also shown that the height-gradient of the ionospheric conductivity plays a very important role for charge separation in the ionosphere, the effect of which intensifies the eastward equatorial electrojet on the dayside.

Multiplet structure and charge distributions in silicon and germanium dimers

Calculations of binding-energy curves and charge distributions have been carried out for low-lying states of ${\mathrm{Si}}_{2}$ and ${\mathrm{Ge}}_{2}$ using the local-density-functional formalism. Calculated spectroscopic constants are in good agreement with experiment for the states of ${\mathrm{Si}}_{2}$ which have been identified, so that predictions for other states should be reliable. The binding-energy curves of the two dimers are remarkably similar, as are the $s\ensuremath{-}p$ valence orbitals of silicon and germanium atoms. Charge-density differences are similar to those calculated previously for ${\mathrm{C}}_{2}$ and orbital densities show pronounced differences from results of a recent pseudopotential calculation, even in regions far from the cores.

Ionization energies and electronic structure of N 3P 3Cl 6 as determined by UV photoelectron spectroscopy and the Xα scattered wave method

Ionization energies have been measured for N 3P 3Cl 6 by He I photoelectron spectroscopy and they are compared with values calculated with the overlapping-spheres version of the Xα scattered wave method; the average discrepancy is less than 0.4 eV. The wavefunctions and associated charge distributions are used for assessing models of ring π bonding, and comparisons are made with previous calculations for N 3P 3F 6 and N 4P 4F 8. The calculated charge distributions are related to trends in measured core electron binding energies, and have important implications for the interpretation of Faraday effect measurements on cyclic phosphazenes.