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The electrostatic model, which is widely used to explain π-involved interactions, gives an intuitive picture of these intermolecular interactions and has successfully predicted many phenomena in recent decades. Still, this simple model faces problems in certain cases and it has come under fire in previous studies on π-π stacking interactions. Here, employing ab initio calculations, we have identified several counter examples in aqueous-π systems which cannot be explained adequately using the classical electrostatic model, and revealed the underlying reason. We find strong intermolecular orbital interactions in both aqueous-π hydrogen bond and lone-pair-π interactions, and thus extend the previously proposed new model for π-π stacking to aqueous-π systems: while the electrostatic attraction and dispersion effects are the main driving forces pulling the monomers together, Pauli repulsion plays a role in keeping them apart. Interestingly, the molecular orbitals on the concerned monomers exhibit a weak bonding nature at the equilibrium distance.

Photosynthetic pigment-protein complexes control local chlorophyll (Chl) transition frequencies through a variety of electrostatic and steric forces. Site-directed mutations can modify this local spectroscopic tuning, providing critical insight into native photosynthetic functions and offering the tantalizing prospect of creating rationally designed Chl proteins with customized optical properties. Unfortunately, at present, no proven methods exist for reliably predicting mutation-induced frequency shifts in advance, limiting the method's utility for quantitative applications. Here, we address this challenge by constructing a series of point mutants in the water-soluble chlorophyll protein of Lepidium virginicum and using them to test the reliability of a simple computational protocol for mutation-induced site energy shifts. The protocol uses molecular dynamics to prepare mutant protein structures and the charge density coupling model of Adolphs et al. [Photosynth. Res. 95, 197-209 (2008)] for site energy prediction; a graphical interface that implements the protocol automatically is published online at http://nanohub.org/tools/pigmenthunter. With the exception of a single outlier (presumably due to unexpected structural changes), we find that the calculated frequency shifts match the experiment remarkably well, with an average error of 1.6 nm over a 9 nm spread in wavelengths. We anticipate that the accuracy of the method can be improved in the future with more advanced sampling of mutant protein structures.

Dislocations are not only mechanical features of crystalline materials, but also complex electrostatic features; this has important implications for understanding electrical and optical properties of real semiconductor materials. An edge dislocation in a semiconductor material becomes electrically charged when free electrons migrate to the dangling bonds along the core; the line charge along the core is then partially screened by the background free carrier concentration. In this work we consider the atomistic structure of an edge dislocation in a technologically important compound semiconductor material, GaN, and develop a complete continuum model of the electrostatic structure of the dislocation. The atomistic analysis is used to determine the maximum charged state of the dislocation core according to first principles electronic structure analysis; the maximum charged state is then expressed as a continuum electrostatic potential. By formulating an energy balance model as a function of the incremental filling of electron acceptor sites, the equilibrium electrostatic state of the dislocation is then determined. This electrostatic state can then be used as the basis for predictive models of electrical scattering or optical absorption.

The range of possible combinations of the components of the electronic-polarizability tensors of oxygen and iodine ions and the effective charges of these ions is established on the basis of the experimental study of the parameters of the electric-field gradient tensor at 7Li nuclei in an α-LiIO3 crystal and the calculation of the electric-field gradient from the classical electrostatic model. The I-O bonds in α-LiIO3 are shown to be mixed ionic-covalent bonds with low ionicity. Spontaneous polarization of the crystal is estimated.

In this paper, a three-center electrostatic model of diatomic bonds was put forward, as well as four physical parameter expressions of effective bonding charges, which support this model. Thus, a semi-empirical method, used to quantitatively study some physical chemistry phenomena, was raised. With the upper method in the article, many theoretical formulas were deduced for such important physical parameters as bond moment, force constant, field gradient and nonlinear optical coefficient of crystals. The available calculated values of every physical parameter basically conformed to its measured magnitude on the condition that parameters were nonadjustable.

The modified electrostatic model is applied to diffusion of 3d to 5d transition metals in nickel and γ-iron. The comparison of experimental and calculated temperature dependence of the diffusion coefficients D permits conclusions with respect to effective charges of the solute atoms. The comparison with the results of diffusion in copper permits the estimation of D(T) for systems where no reliable data are available.

The modified electrostatic model is applied to diffusion of 3d–5d transition metals in noble metals. The comparison of experimental and calculated temperature dependence of the diffusion coefficients permits conclusions with respect to effective charges of solute atoms.

Homolytic bond dissociation energy (BDE) for CH and CX (X = F, Cl, or Br) bonds in polyhalogen methanes was successfully correlated with a two-parameter model describing the repulsion energy of the bonding electron pair with other electrons and its attraction with nuclei, respectively. BDE values for seven molecules were predicted and compared with those calculated by a DFT method. Copyright © 2006 John Wiley & Sons, Ltd.

Possible combinations of the electronic polarizability tensor components for oxygen and tantalum ions have been established based on the analysis of the refraction coefficients of LiТаO3 crystal in the far-IR region. The local electric field on structurally nonequivalent ions in the LiТаO3 unit cell was calculated within the modified point-multipole model. A combination of the electronic polarizability tensor components for oxygen and tantalum ions and their effective charges is established, which provides a good correspondence of the calculation results with the experimental data on LiТаO3 crystals obtained by 7Li nuclear magnetic resonance and 181Та nuclear quadrupole resonance and with the known value of the crystal spontaneous polarization.

The modified electrostatic model (Neumann and Tolle 1995) is applied to the impurity diffusion in nickel.Z0 = 0.4 is used for the effective charge of the nickel ion.

A two-dimensional electrostatic model for degraded short channel lightly doped drain (LDD)-nMOSFETs is presented. The model is based on a numerical solution of the Poisson equation using the five-point finite difference approximation. The model takes into account all device details including doping profiles and spatial and energy distribution of hot-carrier induced interface traps in the LDD region. Potential and charge distributions within the device in weak (subthreshold) and strong inversion regimes have been extensively studied. The validation of the model has been carried out through comparison between simulated I-V characteristics in the linear region and published experimental data. The results obtained have shown that the drain current is greatly affected by the energy distribution of interface traps, especially in the low gate voltage range (near-threshold and subthreshold).

An interesting observation reported that the critical micelle concentrations of an ionic amphiphilic block copolymer increased with the salt concentration. Numerical solutions of the Poisson–Boltzm...

An electrostatic model is proposed to calculate the formation energy ΔЕ of linear HCCH…Х– (X = F, Cl, Br, I) hydrogen-bonded anionic complexes between a halide ion and an acetylene molecule. The potential energy surface (PES) in this model includes four kinds of interaction in the HCCH…Х– system, namely, electrostatic (Coulombic), polarization, dispersive, and exchange repulsion interactions. An analytical expression for the formation energy ΔЕ of the complexes is obtained, and the PES parameters necessary for calculating ΔЕ are determined. The calculated ΔЕ values are in good agreement with ab initio data from the literature. The relative contributions from the different types of interactions to ΔЕ are estimated and analyzed. The electrostatic (Coulombic) interaction makes the main contribution to the formation energy of HCCH…Х– clusters.

Molecular dynamics (MD) simulations results are herein incorporated into an electrostatic model used to determine the structure of an effective polymer-based antidote to the anticoagulant fondaparinux. In silico data for the polymer or its cationic binding groups has not, up to now, been available, and experimental data on the structure of the polymer-fondaparinux complex is extremely limited. Consequently, the task of optimizing the polymer structure is a daunting challenge. MD simulations provided a means to gain microscopic information on the interactions of the binding groups and fondaparinux that would have otherwise been inaccessible. This was used to refine the electrostatic model and improve the quantitative model predictions of binding affinity. Once refined, the model provided guidelines to improve electrostatic forces between candidate polymers and fondaparinux in order to increase association rate constants.

This paper presents an analytical solution to the electrostatic actuation of an asymmetric combdrive in out-of-plane and torsional motions. The exact solutions to force in the out-of-plane motion and the integral for torque in the torsional motion are obtained. The dependence of the peak force on the thickness of the movable fingers and the amount of overlap of the combs is given in closed form. Using our model, the shift of the natural resonant frequency due to a dc bias is analyzed. Furthermore, our solution also applies to the in-plane motion of an in-plane interdigitated combdrive. We found that an in-plane interdigitated combdrive generates a constant force within 0.1% when the minimum initial engagement length of the combs is twice the separation gap.

We present a simple, efficient, and flexible three-dimensional electrostatic model for calculating the magnitude and direction of the electric field from the ground to the base of the ionosphere for a given thunderstorm charge configuration, with the aim of evaluating the possibility for sprite inception. The model is based on a method-of-images solution to Poisson's equation, assuming near vacuum conditions and with perfectly conducting upper and lower boundaries. A dipole electrical structure within each thundercloud is assumed, with a screening (shielding) charge above the cloud. The charge centers (main positive, main negative, and screening charge) are modeled with average structural characteristics of summer and winter thunderstorms. To simulate a positive or negative cloud-to-ground lightning discharge, the main positive or main negative charge center, respectively, is removed from the domain. The computed electric potential at each grid point is converted to the electric field and is compared against the value of the conventional breakdown field to obtain an indication of the possibility of electrical breakdown and hence the possibility of sprite inception. This simple model is particularly useful for performing a sensitivity study with respect to variation in thunderstorm cell charge configuration, with no assumption of symmetry in the horizontal or vertical directions. Implications of the presence of neighboring clouds at different relative stages of development on the possibility of sprite inception and on the displacement of sprites from the location of the parent thunderstorm are also examined, as well as clouds with inverted dipole charge configuration.