Showing papers on "Charge density published in 1978"
TL;DR: If the fractional increase in capacitance found here is a good approximation to that of biological membranes, nonlinear capacitative charge displacement derived from electrostriction is expected to be less than 1% of the total gating charge displacement found in squid axons.
230 citations
TL;DR: In this article, a method for solving the Green's-function equations describing an isolated localized defect in an otherwise perfect crystal was developed, which yields a charge density in sufficient detail to allow recalculation of the potential and iteration to self-consistency.
Abstract: We have developed a method for solving the Green's-function equations describing an isolated localized defect in an otherwise perfect crystal. It yields a charge density in sufficinet detail to allow recalculation of the potential and iteration to self-consistency. The method is applied to the ideal (unrelaxed) vacancy in silicon, in the ionic-pseudopotential, local-exchange-correlation approximation.
181 citations
TL;DR: In this article, the mean field theory of the Peierls instability for the Frohlich Hamiltonian of a one-dimensional electronic system which interacts with lattice modes of vibration is discussed and the properties of periodic lattice distortions and the accompanying charge density waves which result from the instability are described.
173 citations
TL;DR: In this article, the Debye-Huckel screened Coulomb interaction was used to estimate the excluded volume in polyelectrolytes. But the assumption that the cooperative interaction of neighboring segment pairs is not important because the interaction is weak was criticised.
Abstract: Straightforward application of the Debye-Huckel screened Coulomb interaction to the excluded volume effect in polyelectrolytes is known to give estimates of the segment-segment excluded volume that may be too large by several orders of magnitude. It is argued that the major defect in this application lies in a conventional assumption of excluded volume theory that does not apply to charge interactions, rather than in the electrostatic potential itself. This assumption is that the cooperative interaction of neighboring segment pairs is unimportant because the interaction is weak. An attempt is made to restore the applicability of this assumption through the choice of a segment that incorporates many monomer units. The segment is modeled as a rod and is required to be longer than the Debye screening length. A numerical value has to be chosen for the linear charge density but not for the contour length of the rod. The present work reproduces the conventional formula for the excluded volume if the charge density is very low, but much smaller values are found for practical applications. An illustrative application is made to poly(acry1ic acid), for which the charge density is chosen to be about twice the structural value for the extended configuration, in agreement with previous work. The Debye-Huckel interaction is found to work quite well.
165 citations
15 Jun 1978
TL;DR: In this paper, the authors used a general computer program to solve complex solution and surface reaction equilibria for a single or several types of surface groups with solute ions and showed that the surface ion binding of electrolytes is a major contributing reaction for surface charge development.
Abstract: Measurement of the specific conductance, pH, and zeta potential of latex dispersions upon titration with acid or base have been used by several workers to determine the number and nature of the surface ionizable groups. The ionization of latexes with single or several types of surface groups is modified by the interaction of the surface charge and potential with solute ions and is often complex and difficult to interpret in a quantitative manner. The solution of this problem requires (a) accurate estimates of the chemical and surface parameters of the particular latex dispersion, and (b) a reliable model for the potential and charge distribution at the latex/water interface. We describe the results of calculations using a general computer program for solving complex solution and surface reaction equilibria. The surface ion binding of electrolytes is shown to be a major contributing reaction for surface charge development and a new double extrapolation method for determining the intrinsic equilibrium constants for simple ionization and complex ionization reactions is outlined. Simulated titrations in which pH, specific conductivity, κ, and zeta potential, ζ, are estimated for each addition of base or acid are given and compared to reported results.
165 citations
TL;DR: In this paper, Fourier analysis applied to the recently introduced thermal pulse method yields new and unique relations between the time-dependent pyroelectric response of a thin specimen and the Fourier coefficients of the charge or polarization distribution across its thickness.
Abstract: Fourier analysis applied to the recently introduced thermal pulse method yields new and unique relations between the time-dependent pyroelectric response of a thin specimen and the Fourier coefficients of the charge or polarization distribution across its thickness. The new analysis is applied illustratively to thermal pulse data for a vinylidene fluoride copolymer electret.
156 citations
TL;DR: Fermi-surface instability leading to charge density waves is a common malady in anisotropic metals, and there is now evidence that it also infects isotropic ones.
Abstract: Fermi-surface instability leading to charge density waves is a common malady in anisotropic metals, and there is now evidence that it also infects isotropic ones.
139 citations
TL;DR: A particularly promising charge-shift chromophore is the 4-(p-aminostyryl) pyridinium cation, which is consistent with more rigorous calculations on several selected systems as well as with the available experimental data.
Abstract: The chromophores of a series of known and unknown probes of membrane potential are subjected to molecular orbital calculations. These calculations are used to characterize the charge distribution and excitation-induced shift of electron density in the chromophores. This is used to predict or rationalize the magnitude of an electrochromic response to membrane potential. The predictions are consistent with more rigorous calculations on several selected systems as well as with the available experimental data. Emerging from the survey is a variation on previously considered forms of electrochromism involving a simple migration of the charge in an ionic chromophore. The intrinsic amphipathic structures of some of these systems may make them especially well suited for the construction of well oriented, highly responsive probes. A particularly promising charge-shift chromophore is the 4-(p-aminostyryl) pyridinium cation.
137 citations
TL;DR: In this article, coupled-state calculations of proton-hydrogen-atom scattering using a scaled hydrogenic basis set have been performed, and the results are reported on in this paper.
Abstract: Coupled-state calculations of proton---hydrogen-atom scattering using a scaled hydrogenic basis set have been performed, and the results are reported on in this paper. Thirty-five basis functions, centered about each proton, were included in the expansion of the electron wave function. Cross sections for direct excitation and charge transfer to the $n=1, 2, \mathrm{and} 3$ levels, and for ionization, have been calculated. The results for ionization indicate that charge transfer to the continuum dominates over direct ionization at proton energies below about 60 keV. The charge distribution has been plotted as a function of time at an energy of 40 keV and impact parameter of 1.5 a.u.; the plot illustrates the considerable distortion of the electron cloud caused by the passing proton.
134 citations
TL;DR: The crystal structure of NbSe3 has been refined from single crystal X-ray diffraction data as discussed by the authors, which shows that the 145K transition in the electrical resistivity is not accompanied by a structural distortion.
Abstract: The crystal structure of NbSe3 has been refined from single crystal X-ray diffraction data. It has a monoclinic symmetry with lattice parameters: a=10.009 AA, b=3.4805 AA, c=15.629 AA, beta =109.47 AA, space group P21/m and six formulae per unit cell. The crystal structure of NbSe3 as determined at 100K shows that the 145K transition in the electrical resistivity is not accompanied by a structural distortion. Except for the decrease due to thermal contraction all interatomic distances are found to be the same. This is compatible with the proposed model of the charge-density-waves formation which has been put forward in order to explain the physical properties of the 145K transition. Electron diffraction pictures taken above and below the transition give direct evidence of the charge-density-waves formation at the transition. At 120K in agreement with Tsutsumi et al. (1977) the pictures contain superstructure spots at the (h,k+or-0.243, l) positions. Contrary to what has been reported by the same authors, the authors have found that at 3K above the transition the electron diffraction pictures do not contain the diffuse scattering streaks corresponding to the planes at k'=k+or-0.243, which would indicate fluctuations of the CDW above the transition.
118 citations
TL;DR: In this paper, the authors used self-consistent pseudopotential techniques, together with a superlattice geometry, to investigate the detailed electronic structure of the (110) interfaces of Ge-GaAs and AlAs-GAAs.
Abstract: Self-consistent pseudopotential techniques, together with a superlattice geometry, are used to investigate the detailed electronic structure of the (110) interfaces of Ge-GaAs and AlAs-GaAs. For Ge-GaAs six types of interface states are found, all lying below the thermal gap. No interface states are found in AlAs-GaAs. For each interface the total charge density, self-consistent potential, projected band structure, and local density of states are presented. The interface states in Ge-GaAs are discussed in detail. We also present results for the conduction- and valence-band discontinuities at these interfaces, discuss superlattice states in AlAs-GaAs, and suggest possible relaxation at the Ge-GaAs (110) interface.
TL;DR: In this paper, the recently reported phase transitions of Mo(001) and W(001), in terms of surface charge-density waves, are discussed and the expected two-dimensional critical behaviour is also investigated.
TL;DR: In this article, the electronic properties of the regular graphite lattice are investigated within self-consistent LCAO (linear combination of atomic orbitals) scheme based as a modified extended-H\"uckel approximation.
Abstract: The electronic properties of the regular graphite lattice are investigated within self-consistent LCAO (linear combination of atomic orbitals) scheme based as a modified extended-H\"uckel approximation. The band structure and interband transition energies agree favorably with previous first-principles calculations. Good agreement with experimental data on the density of valence states, energetic position of the lowest conduction states, equilibrium unit-cell parameters, cohesive energy and vibration force constants, is obtained. The McClure band parameters that were previously adjusted to obtain agreement with Fermi-surface data and the electronic specific heat, are reasonably reproduced. The charge distribution and bonding characteristics of the covalent graphite structure, are discussed. The same calculation scheme is used in part II of this article (following paper) to discuss properties associated with point defects in graphite. The correlation between the electronic properties of the regular and point-defect-containing lattice is studied.
TL;DR: In this article, the lateral motion of charges along thin films of polyethylene terephthalate (PET) in air at 40% humidity was measured and a sensitive, high-resolution induction probe coupled to a computer was used to scan the sample in a raster mode.
Abstract: Measurements are reported on the lateral motion of charges along thin films of polyethylene terephthalate (PET) in air at 40% humidity. A sensitive, high-resolution induction probe coupled to a computer is used to scan the sample in a raster mode. Thus it is possible to produce not only line scans of the charge distribution across the film at any time, but also to display the charge as contour or relief maps as well. The behaviour of charge can thus be studied in more detail than previously. It is established that charges of either sign deposited from a corona source move laterally according to a diffusion law although there is some evidence that this motion may also be controlled by the electric fields induced. The diffusion coefficient is of order 10-9 m2 s-1 with an activation energy of 1.5 eV and is much greater than the coefficient for the diffusion of neutral gases in the polymer. The diffusion is probably within the bulk of the polymer but washing in deionised water induces a much higher rate or diffusion which is probably a true surface phenomenon.
TL;DR: In this paper, the scalar relativistic approximation (SRA) method has been proposed for the approximate calculation of relativism effects in atoms and solids, where the spin-orbit coupling term appearing in Dirac's equation is dropped; occasionally the minority component of the wave function is also neglected in defining the charge density.
Abstract: A new method has recently been proposed for the approximate calculation of relativistic effects in atoms and solids. In this method, which is called the scalar relativistic approximation (SRA), the spin-orbit coupling term appearing in Dirac's equation is dropped; occasionally the minority component of the wave function is also neglected in defining the charge density. We propose here another derivation of the SRA that clarifies the approximations. A simple analytical treatment of the SRA for the hydrogen atom is given, and, as an example of the application of the SRA to the calculation of atomic states, results of self-consistent, local-density calculations for the ytterbium atom are given. The results show that, except for the spin-orbit splitting, relativistic effects (due to the Darwin and mass-velocity terms) are taken into account by the SRA very well.
TL;DR: In this paper, the Schlier-Farnsworth-Levine pairing model was used to reconstruct the Si(100) surface with a monolayer of atomic hydrogen chemisorbed to it.
TL;DR: In this article, a pulsed NMR study on a single crystal of 2H-NbSe2 at atmospheric pressure and under hydrostatic pressure of 21 kbar in the temperature range 4.2-273K is presented.
Abstract: Presents a pulsed NMR study on a single crystal of 2H-NbSe2 at atmospheric pressure and under hydrostatic pressure of 21 kbar in the temperature range 4.2-273K. Analysis of Knight shift (KS) and nuclear spin-lattice relaxation (NSLR) time data in the normal state are consistent with N(EF)=2.4 states/eV spin and an admixture of 40% of dxy and dx2-y2 wavefunctions in the dz2 band. The product T1T=500+or-100 ms K was found constant in the temperature range 4.2-77K and pressure independent; measurements at the 'magic angle' indicate an orbital contribution (T1T)-1 approximately=0.9+or-0.9 (sK)-1. The results are consistent with the onset of incommensurate charge density waves (ICDW) at T0=33K at P=1 bar and T0=26K at 21 kbar. Below T0, the lineshapes of the m to m-1 transitions agree with a local distribution of KS and EFG respecting the symmetry of a triple ICDW with a maximum value of 9% for the redistribution of conduction electrons within an atomic cell. Above T0, nuclear spin-spin relaxation measurements demonstrate that the observed pretransitional broadening of the lines is due to static CDW fluctuations, induced by impurities.
TL;DR: In this article, a sine-Gordon soliton through an impurity potential is calculated and the electric field and temperature dependence of a charge-density wave pinned by impurities are investigated.
Abstract: In the presence of impurity potentials which couple directly to the phase of the charge-density waves the ground state as well as soliton excitations are pinned. The quantum-mechanical tunneling of a sine-Gordon soliton through an impurity potential is calculated. The small tunneling probability for even a moderate impurity potential means that the conductivity due to solitons will be greatly reduced. We also study the electric field and temperature dependence of a charge-density wave pinned by impurities when quasiclassical tunneling is taken into account. The temperature dependence is found to be dominated by simple thermal excitation and the conductivity is activated in both the strong- and weak-pinning limits.
TL;DR: The model successfully predicts the transition from a predominantly screening situation to a predominantly binding situation, which was observed experimentally when negative surface charge density was decreased in nerve.
Abstract: To arrive at a clear and atomically realistic representation of the process of ionic screening, a model with the following necessary and justifiable constraints was devised. 1) The minimum internuclear distance (IND) between a negative site on the membrane and a cation screening the site is equal to the sum of the site's "equivalent" radius (rs) + the diameter of a water molecule (approximately 2.8 A) + crystal radius of the cation (rc). 2) The average value for the dielectric constant (D) over IND is given by D approximately 80 ((IND - rs - rc)/IND). When this simple atomic model for ionic screening is employed in conjunction with equilibrium ion-selectivity theory, it is possible to predict quantitatively, from coulombic energy calculations, the secondary stereospecific actions of certain alkaline-earth cations as well as the predominant screening effect of these divalent cations at the surfaces of different types of membranes. The model also successfully predicts the transition from a predominantly screening situation to a predominantly binding situation, which was observed experimentally when negative surface charge density was decreased in nerve.
TL;DR: In this article, the X-ray structure factors of CaO, SrO and BaO were measured at 293 K from single crystals and analyzed together with the data of Sanger [Acta Cryst (1969), A25, 694-702] on MgO.
Abstract: Accurate X-ray structure factors of CaO, SrO and BaO were measured at 293 K from single crystals and analysed together with the data of Sanger [Acta Cryst (1969), A25, 694-702] on MgO The oxygen ion is seen to suffer an average compression and a fourth-order cubic harmonic type deformation, as compared to the atomic superposition model, yielding a lower average charge density in the surrounding region and a charge transfer from [111] to the [100] direction These features strengthen with increasing atomic number of the cation Mg and Ca show a weak broadening About nine electrons are localized around the oxygen position The tenth electron of O2- is more widely distributed The electron counts of the cation correspond most closely to Mg+, Ca2+, Sr2+ and Ba2+ The results confirm the dominance of ionic character and increase of ionicity with increasing atomic number of the cation
TL;DR: In this article, the mode of adsorption of poly(oxyethylene), poly(acrylic acid) (PAA), poly 4-vinylpyridine (PVP), and isobutyric acid (IBA) at the charged aerosil silica-aqueous electrolyte interface was studied by surface charge, adsorbing density, and electrophoresis investigations.
Abstract: Polymer molecules can undergo considerable conformational changes upon adsorption at solid-liquid interfaces. Such changes frequently affect the properties of polymer-modified systems and therefore have become a matter of growing interest. The mode of adsorption of poly(oxyethylene) (PEO), poly(acrylic acid) (PAA), poly(4-vinylpyridine) (PVP), and isobutyric acid (IBA) at the charged aerosil silica-aqueous electrolyte interface was studied by surface charge, adsorption density, and electrophoresis investigations. Due to the dissociation of surface silanol groups, the silica surface becomes increasingly negatively charged when the suspension pH is raised above approx. 3.5. Adsorption of PEO reduces the surface charge density considerably. While PEO is only partially desorbed from a silica surface with increasing surface charge, complete desorption of PAA and of IBA occurs along with their dissociation to form anions. Protonated PVP is readily adsorbed around the point of zero change, the adsorption density diminishing with decreasing pH. 19 references.
TL;DR: In this article, the authors examined how the thermal pulse technique for determining spatial charge distribution in charged polymer foils is affected by inaccuracies of the measuring process and developed a theoretical model for thermal equalization processes which is in agreement with the measured temperature transients.
Abstract: We examine how the thermal‐pulse technique for determining spatial charge distribution in charged polymer foils is affected by inaccuracies of the measuring process. A theoretical model is developed for thermal equalization processes which is in agreement with the measured temperature transients. Using this model, we show by computer simulation that even for a measurement inaccuracy of less than 1% the obtainable information consists of only the first moment of the charge distribution and the first few Fourier coefficients.
TL;DR: In this paper, closed-form solutions for the charge density and current density in the vicinity of dislocation or a surface which pierces a junction at right angles were obtained for the reduction in luminescence and increase in junction current.
Abstract: Closed‐form solutions (integral representations) are obtained for the charge density and current density in the vicinity of a dislocation or a surface which pierces a junction at right angles. The total reduction in luminescence and increase in junction current are obtained as functions of two dimensionless ratios, e, the recombination‐length/diffusion‐length ratio, and η, the radius‐of‐dislocation/diffusion‐length ratio, where recombination length a=D/s is the diffusion constant over surface‐recombination velocity.
TL;DR: In this paper, the authors obtained wavefunctions as a function of geometry for an O atom bonded to Ni clusters (consisting of one to five atoms) designed to model bonding to the (100) surface of Ni.
TL;DR: In this paper, the long-range behavior of the electronic charge density of ground-state atoms is considered and an exponentially decreasing function is derived, which depends on the ionization potential and an effective nuclear charge.
Abstract: The long-range behavior of the electronic charge density of ground-state atoms is considered. A rigorous upper bound to this function is derived and is found to be an exponentially decreasing function, which depends on the ionization potential and an effective nuclear charge.
TL;DR: In this paper, the authors examined the competition between commensurability pinning and impurity pinning on the existence of the long range order at absolute zero in the case of weak impurity pins of the one-dimensional charge density wave and showed that near the boundary of the CDW state and CDG state the average of the formation energy of a localized excitation (a soliton) is decreased whereas that of a extended excitation remains essentially unchanged.
Abstract: Competition between the commensurability pinning and the impurity pinning on the existence of the long range order is examined at absolute zero in the case of the weak impurity pinning of the one-dimensional charge density wave. There exists a critical value of the commensurability energy, l 0 / d =1.4, which separates the state with long range order (charge density wave (CDW) state) and that without it (charge density glass (CDG) state). Here l 0 and d are the domain size in the absence of commensurability energy and the size of a soliton in the absence of the impurity potential respectively. It is argued that near the boundary of the CDW state and CDG state the average of the formation energy of a localized excitation (a soliton) is decreased whereas that of a extended excitation (a phason) remain essentially unchanged.
TL;DR: In this paper, a simple method of obtaining integral representations of the electrostatic potential, the induced surface charge density, and the image potential for a point charge in a three-dielectric medium with infinite planar interfaces is presented.
Abstract: A simple method of obtaining integral representations of the electrostatic potential, the induced surface charge density, and the image potential for a point charge in a three‐dielectric medium with infinite planar interfaces is presented. The total induced charge at the interfaces is readily evaluated. Numerical results for the image potential in several illustrative cases are also shown. The case of a point charge between two grounded conducting plates becomes a special limiting case of the present problem.