Showing papers on "Charge (physics) published in 1981"
TL;DR: In this paper, a theory of molecular structure is presented, which demonstrates that the concepts of atoms and bonds may be rigorously defined and given physical expression in terms of the topological properties of the observable distribution of charge for a molecular system.
Abstract: A theory of molecular structure is presented. The theory demonstrates that the concepts of atoms and bonds may be rigorously defined and given physical expression in terms of the topological properties of the observable distribution of charge for a molecular system. As a consequence of these definitions, one in turn obtains a definition of structure and a predictive theory of structural stability. The theory is linked to quantum mechanics by demonstrating that the atoms so defined represent a class of open quantum subsystems with a unique set of variationally defined properties.
505 citations
TL;DR: In this article, the Coulomb potentials and fields in infinite point charge lattices are represented by series expansions in real and reciprocal space using a method similar to that devised by Bertaut.
Abstract: The Coulomb potentials and fields in infinite point charge lattices are represented by series expansions in real and reciprocal space using a method similar to that devised by Bertaut. A systematic investigation is made into the relative convergence characteristics of series derived by varying the charge spreading function which is required in the theory. A number of formulas which are already in use are compared with new expressions derived by this method.
206 citations
199 citations
TL;DR: In this article, the effect of using several approximations is considered (i) for representing the isolated molecules (which determine the electrostatic and polarization terms), and (ii) for evaluating the shortrange repulsion term.
Abstract: Some aspects of the use of simplified formulas for the evaluation the interaction energy between two molecules is discussed. This energy is obtained as the sum of four terms: electrostatic, polarization, dispersion, and short-range (exponentially decreasing) repulsion. The effect of using several approximations is considered (i) for representing the charge distributions of the isolated molecules (which determine the electrostatic and polarization terms), and (ii) for evaluating the short-range repulsion term. The various charge distributions considered are semiempirical atomic net charges (Del Re + Pariser-Parr), atomic charges and dipoles (CNDO) and corresponding “effective” atomic charges, and many-centered multipole distributions obtained from ab initio SCF calculations (charges, dipoles, and quadrupoles located on the atoms and the middles of segments joining pairs of atoms, whether chemically bonded or not). As concerns the short-range repulsion, the various procedures considered are a sum of atom-atom terms, a sum of bond-bond terms, and the use of anisotropic van der Waals radii for heteroatoms (oxygen and nitrogen). In all cases, the dispersion energy is obtained as a sum of atom-atom terms (of the R−6 type). These various procedures are checked in the case of the interactions between nucleic acid bases, for two rather different kinds of configurations, namely, hydrogen bonded and stacked. This comparison reveals a rather complicated picture, namely the results got from the various levels of approximation of the molecular charge distribution lead to different degrees of agreement according to different situations, e.g., for guanine-cytosine interactions, qualitative agreement is found between the various methods as concerns the relative order of stacked and hydrogen bonded situations, while agreement is much less satisfactory for adenine-uracile interactions. One of the main conclusions is that a sufficiently sophisticated representation of the molecular charge distribution is required in order to get reliable results for all possible configurations of a complex. Such comparative studies should bring significant help as concerns the development of the reliable simplified procedures for evaluating intermolecular interaction energies.
135 citations
126 citations
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95 citations
TL;DR: In this article, a new method is presented for the calculation of partition coefficients of solutes in water lipid systems based on the charge densities of the atoms as determined by quantum mechanical methods.
Abstract: A new method is presented for the calculation of partition coefficients of solutes in water lipid systems. Log P values are calculated based on the charge densities of the atoms as determined by quantum mechanical methods. In this article, the results have been obtained from charge densities calculated by two methods: MINDO/3 and Huckel-type calculation based primarily on topology. Results are favorably compared with those obtained by fragment analysis.
91 citations
1 Jan 1981
69 citations
TL;DR: In this article, a secondary ion recoil source was used to study charge transfer and ionization in collisions of arXiv:1511.9000v on Ne at projectile energies between 100 and 1100 eV per projectile charge.
Abstract: A secondary-ion recoil source was used to study charge transfer and ionization in collisions of ${\mathrm{Ar}}^{q+} (2\ensuremath{\le}q\ensuremath{\le}9)$ on Ne at projectile energies between 100 and 1100 eV per projectile charge. Two experimental methods are presented. With the first one we measure cross sections for electron capture by detecting both the initial and final charge states of the Ar ions. With the second method we measure, in addition to those parameters, the charge state of the Ne ions after the reaction. This three-parameter method allows us to distinguish among various competing reaction mechanisms and to measure cross sections for single- and multiple-electron capture, ionization, and transfer ionization. We find that the cross sections for ionization without simultaneous capture are negligibly small, whereas those for transfer ionization are quite important in several cases.
TL;DR: In this paper, a numerical method for calculating electric fields very accurately in configurations including voluime resistance or surface resistance is described, which is based on the charge simulation method (CSM).
Abstract: This paper describes a numerical method for calculating electric fields very accurately in configurations including voluime resistance or surface resistance. The principle of the method is to incorporate the field effect of the true charge caused by conductivity in that of complex fictitious charges by the charge simulation method (CSM). CSM with complex charges for computing multi-phase AC fields is also described with a calculated example. Results are given for comparison with analytical expressions and for a disc-type gas insulation spacer having either volume resistance or surface resistance.
TL;DR: In this article, a new atomic orbital method was proposed for charge transfer through prechosen time-dependent amplitudes which equal the'real' amplitudes only at large times, where the target excitation and ionisation amplitudes are found variationally but constrained to produce consistent charge transfer amplitudes.
Abstract: In a series of recent papers the authors have studied the inner-shell direct ionisation and charge transfer processes that occur when a light ion with nuclear charge Zp, collides with a target atom, nuclear charge ZT They used a single-centred expansion (SCE) method, expanding the single-electron wavefunctions in a set of target-centred Hilbert states This method is inaccurate if charge transfer is an important channel for electron flux loss and is thus generally restricted to the asymmetric region, Zp<
TL;DR: In this paper, the one-loop contributions to the amplitude A and B in the standard electroweak gauge model were computed. But they were not considered in this paper, and the result is of importance if all mass effects are to be correctly taken into account.
Abstract: We compute exactly all the one-loop contributions to the amplitude A..-->..B..gamma.., where A and B are fermions of the same charge, but different flavor, in the standard electroweak gauge model. The result is of importance if all mass effects are to be correctly taken into account.
IBM1
TL;DR: In this article, the electronic structures of SrTiO3 with Fe3+, Fe4+ and Fe5+ ions were investigated using the Xα cluster approach, and the ground-state eigenvalues showed the lower Fe acceptor level, of t2g↓ symmetry, localized inside the Sr TiO3 band gap.
TL;DR: In this paper, it is suggested that the so-called charge exchange model for field desorption in fact comprises two alternative mechanisms between which we may discriminate theoretically, and possibly experimentally.
TL;DR: In this paper, the stability of the Schwarzschild interior solution is enhanced by the inclusion of charge, and an increase in the charge further reduces the critical radius for which instability sets in.
Abstract: The coupled Einstein-Maxwell field equations are solved by quadratures for spherically symmetric static systems containing charge. In particular, we show how interior metrics can be derived which reduce to classical solutions for neutral distributions of matter when the charge becomes vanishingly small. A number of simple analytic solutions are expressed in order to indicate how charge can change the overall character of these objects. The stability of charged systems is considered. We find the stability of the Schwarzschild interior solution is enhanced by the inclusion of charge, and that an increase in the charge further reduces the critical radius for which instability sets in. The application of this analysis to the solution of Pant and Sah indicates their model is unstable.
TL;DR: In this paper, the authors describe how to choose the most stable of several equilibrium states that may exist in a liquid-crystal cell at the same voltage V or charge Q. The relative stability of various equilibrium states can be compared by plotting G against V or F against Q.
Abstract: We describe how to choose the most stable of several equilibrium states that may exist in a liquid‐crystal cell at the same voltage V (or charge Q). Among states that exist at the same charge Q, the state with the lowest total free energy F is the most stable. Among states that exist at the same voltage V, the state with the lowest electric Gibbs function (F−QV) is the most stable. Thus the relative stability of various equilibrium states can be compared by plotting G against V or F against Q. An example is given to illustrate the importance of a correct pairing of thermodynamic functions and independent variables.
TL;DR: In this article, it was shown that SU(5) and SO(10) grand unified theories are almost uniquely chosen under a few reasonable assumptions, such as the fact that there exist only left-handed particles in an SU(2) doublet and their antiparticles in a SU(1) singlet.
Abstract: We will prove that SU(5) and SO(10) grand unified theories are almost uniquely chosen under a few reasonable assumptions. The main ansatz is that there exist only left-handed particles in an SU(2) doublet and their antiparticles in an SU(2) singlet. For the case of a single-multiplet unification, SO(10) is unique, using the facts that the charge of the d quark is not neutral and the theory should be anomaly free. For the case of two-multiplet unification, SU(5) is unique among SU(N) (N< or =500). The color group is effectively determined as the standard SU(3) with triplets of colored quarks. Quark charges must be the standard 2/3 and -1/3. No unifying simple group exists for G(horizontal) x G(GUT) under the assumptions above. For the case of SU(5), the cancellation of the triangle anomaly emerges as a consequence rather than a hypothesis.
TL;DR: In this paper, the laws of motion for a point-like nonabelian charge are derived from energy and momentum conservation and covariant charge conservation following a procedure first introduced by Mathisson.
TL;DR: In this paper, the measurements and calculations of the charge, spin and momentum density of the metallic elements Ti to Ni are examined and the Compton profiles (momentum density) and X-ray scattering factors (charge density) are shown to provide direct determination of the cohesive energy.
Abstract: The measurements and calculations of the charge, spin and momentum density of the metallic elements Ti to Ni are examined. Both the Compton profiles (momentum density) and X-ray scattering factors (charge density) are shown to provide a direct determination of the cohesive energy. It generally appears that the 3d spin density is contracted relative to the free atom while the 3d charge density builds up at the Wigner–Seitz cell boundary relative to the free atom particularly near the bottom of the band. No theoretical calculation is available which evaluates charge, spin and momentum density as well as cohesive energy. In addition, a significant disparity between theory and experiment exists for the momentum and charge density anisotropies in the b.c.c. metals. Suggested areas for further work are given.
TL;DR: In this paper, the charge densities of the Reid soft core model and the Coulomb interaction between the two protons in the soft core are compared to the "experimental" one obtained by fitting the experimental form factor data after having approximately removed the effect of nucleon finite size.
Abstract: The charge densities of $^{3}\mathrm{H}$ and $^{3}\mathrm{He}$ are computed for several potential models. These densities are further broken down into isospin components and into components from the $S$, ${S}^{\ensuremath{'}}$, and $D$ states. Wave functions for these states are plotted in order to illustrate the structure seen in the densities. Inclusion of nucleon finite size eliminates the fine structure seen in the point nucleon cases. Form factors corresponding to those densities are also calculated. The inclusion of a Coulomb interaction between the two protons in $^{3}\mathrm{He}$ is seen to produce a small but nonnegligible change in the density. The theoretical $^{3}\mathrm{He}$ densities for the Reid soft core model are compared to the "experimental" one obtained by fitting the experimental form factor data after having approximately removed the effect of nucleon finite size. The central depression seen in the experimental density is not present in the theoretical ones, and we speculate on this and other discrepancies.[NUCLEAR STRUCTURE Trinucleon system, charge density, wave function components, Coulomb interaction.]
TL;DR: In this article, reaction and charge transfer of H + 2 + Ar to give ArH + and Ar + have been investigated as a function of H+ 2 vibrational quantum state and kinetic energy.
TL;DR: In this paper, a satisfactory molecular perturbed-stationary states treatment of one-electron heteronuclear asymmetric charge transfer is derived, and the electronic translation factors and their inherent switching functions are determined variationally.
Abstract: A satisfactory molecular perturbed-stationary-states treatment of one-electron heteronuclear asymmetric charge transfer is derived. Electronic translation factors and their inherent switching functions are determined variationally. Specific consideration is given to the 2p sigma , 2p pi , 3d sigma , 3d pi and 2s sigma states of the HeH2+ molecular ion.
1 Nov 1981
TL;DR: By Fourier decomposition of the appropriate fluctuation it is possible within the regime of linear response to extend the concept of both thermo-dynamic quantities and transport coefficients to their dependence on both wavelength and frequency as mentioned in this paper.
Abstract: By Fourier decomposition of the appropriate fluctuation it is possible within the regime of linear response to extend the concept of both thermo-dynamic quantities and transport coefficients to their dependence on both wavelength and frequency. Experimentally these generalized macroscopic properties are accessible through neutron diffraction and, as examples, the dependence of the sound speed on wavelength and the diffusion coefficient on time are discussed. Through the molecular dynamics computer method the dependence of the viscosity on wavelength is calculated and applied with spectacular success to predict the dependence of the friction coefficient on the size of a Brownian particle all the way to atomic dimensions. On the other hand, the dielectric constant continuum concept, as applied to a charge or dipole in a cavity, generally fails to predict even the correct field at large distance from the charge. Avoiding the introduction of a cavity cures that problem, but the generalized dielectric constant fails badly in predicting the field at shorter distances from the charge.
TL;DR: In this paper, the Schmid-Schoen expression of 1/F*{sub T{sub Q*} has been shown to be incorrect for dirty superconducting AlEr films in which Er is a pair-breaking magnetic impurity that induces charge relaxation through elastic exchange scattering.
Abstract: The charge-imbalance relaxation rate, 1/F*{sub T{sub Q*}}, has been measured in dirty superconducting AlEr films in which Er is a pair-breaking magnetic impurity that induces charge relaxation through elastic exchange scattering. Measurements were made in the range 0.1 {approx}< {Delta}(T)/k{sub B}T{sub c} {approx}< 1.4 for Er concentrations varying from 21 to 1660 at. ppm that produced estimated exchange scattering rates, {tau}{sub S}{sup -1}, from about 10{sup 9} sec{sup -1} to 5 x 10{sup 10} sec{sup -1}. Measured values of 1/F*{sub T{sub Q*}} were in good agreement with the Schmid-Schoen expression, 1/F*{sub T{sub Q*}}=({pi}{Delta}/4k{sub B}T{sub c}{tau}{sub E}) x (1+2{tau}{sub E}/{tau}{sub S}){sup 1/2}, for {Delta}/k{sub B}T{sub c} {approx}< 0.8, where {tau}{sub E}{sup -1} is the electron-phonon scattering rate estimated from the measured transition temperature. For larger values of {Delta}/k{sub B}T{sub c}, the relaxation rate increased less rapidly with {Delta}. The appropriate Boltzmann equation was solved on a computer to obtain values for 1/F*{sub T{sub Q*}} in the range 0.5 {approx}< T/T{sub c} {approx}< 0.999999. The computed values of 1/F*{sub T{sub Q*}} agreed with several analytic expressions valid for {Delta}/k{sub B}T{sub c} << 1, but not with the experimental data: The computed curves increased more rapidly than linearly with {Delta}/k{sub B}T{sub c} nearmore » T{sub c}, and the shape of the 1/F*{sub T{sub Q*}} vs {Delta}/k{sub B}T{sub c} curves was qualitatively different. This discrepancy suggests that either the generally accepted expression for exchange charge relaxation is incorrect, or that the Boltzmann equation is inappropriate for these calculations.« less
TL;DR: In this article, the radial coupling between the nuclear motion and the electronic structure which induces charge transfer at low energy is discussed, and the utility of the force operator form for computing the coupling between large configuration-interaction wave functions is demonstrated.
Abstract: The calculation of the radial coupling between the nuclear motion and the electronic structure which induces charge transfer at low energy is discussed, and the utility of the force operator form for computing the coupling between large configuration-interaction wave functions is demonstrated. Many properties suggest that such couplings will be useful in constructing the diabatic scattering states; the agreement with available matrix elements computed numerically is excellent.
TL;DR: In this paper, the mean square charge radii and the quadrupole moments of Ca nuclei are discussed in the light of theoretical predictions, and the very peculiar dependence of the charge radi on the mass number between double magic40Ca and double magic48Ca can be ascribed to changes of the nuclear deformation, whereas the volume remains constant for all the Ca isotopes.
Abstract: The mean square charge radii and the quadrupole moments of Ca nuclei are discussed in the light of theoretical predictions. The very peculiar dependence of the charge radii on the mass number between double magic40Ca and double magic48Ca can be ascribed to changes of the nuclear deformation, whereas the volume of the nuclear charge remains constant for all the Ca isotopes. Furthermore, correlations between nuclear charge radii and binding energies are discussed.