Cohesive energy of small metallic particles

The cohesive energy of sodium microparticles is calculated using the density functional formalism. The model particles are formed by a central atom surrounded by successive coordination shells of first neighbours, second neighbours, etc. Maxima in the cohesive energy per atom are obtained for particles with filled coordination shells. The sublimation energy is also studied. Insight is gained on the nature of “magic numbers” observed in the experimental size distribution.     

Effect of element Re on the grain boundary cohesion of α-Fe

The effect of Re segregation on the α-Fe ∑5 [001] （010） grain boundary （GB） is investigated by using a software called DMol and discrete variational method （DVM）. Based on the Rice Wang model, the calculated segregation energy and defect formation energy show that Re is a strong cohesive enhancer. We also calculated the interatomic energy （IE） and bond order （BO） of several atomic pairs to investigate the mechanism of the cohesive effect of Re microscopically and locally. The results show that IEs of atomic pairs formed by those atoms which cross the plane of GB are strengthened due to the segregation of Re, while the BOs of the corresponding pairs are slightly decreased. This discrepancy demonstrates that IE which contains the Hamiltoniaa of interaction between atoms is a good quantity to describe the bonding strength. The analysis suggests that the electronic effect between atomic pair which comes directly from Hamiltonian is the key factor, The charge density is also presented, and the result indicates that the bonding strength between the Fe atoms on the GB is enhanced due to the segregation of Re, which is consistent with the analysis of IE.     

Internal structure of a classical spinning electron

A classical model of the spinning electron in general relativity consisting of a rotating charge distribution with Poincaré stresses is set up. It is made out of a continuous superposition of thin charged shells with differential rotation. Each elementary shell is maintained in stationary equilibrium in the gravitational field created by the others. A class of interior solutions of the Kerr-Newman field is thus obtained. The corresponding stress-energy tensor naturally splits into the sum of two terms. The first one is the Maxwell tensor associated to a rotating charge distribution, and the second one corresponds to a material source having zero energy density everywhere, no radial pressure, and an isotropic transverse stress. These negative pressures or tensions are identified with the cohesive forces introduced by Poincaré to stabilize the Lorentz electron model. They are shown to be the source of a negative gravitational mass density and thereby of the violation of the energy conditions inside the electron.     

A model of phase transitions in double-well Morse potential: Application to hydrogen bond

A model of phase transitions in double-well Morse potential is developed. Application of this model to the hydrogen bond is based on ab initio electron density calculations, which proved that the predominant contribution to the hydrogen bond energy originates from the interaction of proton with the electron shells of hydrogen-bonded atoms. This model uses a double-well Morse potential for proton. Analytical expressions for the hydrogen bond energy and the frequency of O–H stretching vibrations were obtained. Experimental data on the dependence of O–H vibration frequency on the bond length were successfully fitted with model-predicted dependences in classical and quantum mechanics approaches. Unlike empirical exponential function often used previously for dependence of O–H vibration frequency on the hydrogen bond length (Libowitzky, Mon. Chem., 1999, vol.130, 1047), the dependence reported here is theoretically substantiated.     

Macroion effective charge in complex plasmas with regard to microion correlations

In the present paper, features of high-charged macroions screening by microions are analysed in classical asymmetrically charged complex plasmas. We consider a two-component electroneutral system of classical macroions and oppositely charged microions in a spherically symmetrical electroneutral Wigner–Seitz cell with a central macroion in its centre. The present paper is devoted to a problem of a relation between the effective macroion charge and an initial one with regard to a non-linear screening effect and microions correlations. We show how this relation changes with the number of the central macroion charge value on the rise. Characteristics of two different parts of the relation between the effective charge and the initial one are calculated.     

General solvation motifs of a charged linear macroion in an aqueous droplet

ABSTRACT

We explore the solvation patterns of a charged rigid and semi-rigid linear macroion in an aqueous droplet. The solvation patterns are summarised in an empirical ‘phase diagram’ on the parameter space defined by the length of the macroion and its charge density. In the study, we employ molecular dynamics and atomistic modelling. The macroion is represented by a positively charged carbon nanotube. Linear macroion-solvent interactions in droplets are distinct from those of spherical ions because of the interplay among several factors such as the tendency of the solvent to form spherical droplets in order to minimise the surface energy, the constraint on the charge of a spherical droplet imposed by the Rayleigh limit, the solvation energy of the macroion and its length. The combination of all these factors may lead to a variety of solvent distributions along the rigid rod such as asymmetric solvation of the linear macroion, formation of spiky ‘star’-like distribution of solvent, partial wetting of the rod by a droplet. The study provides insight into the solvation of macroions in droplets with applications in electrosprayed macroions and atmospheric aerosols. We also propose a possible path of generating a sequence of nanoparticles of different shapes (spheres, multi-point stars) along a linear macromolecule by exploiting the various solvation patterns.     

Salt-modulated structure of polyelectrolyte-macroion complex fibers

The structure and stability of strongly charged complex fibers, formed by complexation of a single long semi-flexible polyelectrolyte chain and many oppositely charged spherical macroions, are investigated numerically at the ground-state level using a chain-sphere cell model. The model takes into account chain elasticity as well as electrostatic interactions between charged spheres and chain segments. Using a numerical optimization method based on a periodically repeated unit cell, we obtain fiber configurations that minimize the total energy. The optimal fiber configurations exhibit a variety of helical structures for the arrangement of macroions including zig-zag, solenoidal and beads-on-a-string patterns. These structures result from the competition between attraction between spheres and the polyelectrolyte chain (which favors chain wrapping around the spheres), chain bending rigidity and electrostatic repulsion between chain segments (which favor unwrapping of the chain), and the interactions between neighboring sphere-chain complexes which can be attractive or repulsive depending on the system parameters such as salt concentration, macroion charge and chain length per macroion (linker size). At about physiological salt concentration, dense zig-zag patterns are found to be energetically most stable when parameters appropriate for the DNA-histone system in the chromatin fiber are adopted. In fact, the predicted fiber diameter in this regime is found to be around 30 nanometers, which roughly agrees with the thickness observed in in vitro experiments on chromatin. We also find a macroion (histone) density of 5–6 per 11nm which agrees with results from the zig-zag or cross-linker models of chromatin. Since our study deals primarily with a generic chain-sphere model, these findings suggest that structures similar to those found for chromatin should also be observable for polyelectrolyte-macroion complexes formed in solutions of DNA and synthetic nano-colloids of opposite charge. In the ensemble where the mean linear density of spheres on the chain is fixed, the present model predicts a phase separation at intermediate salt concentrations into a densely packed complex phase and a dilute phase.     

Effect of the non‐linear screening on a modification of the Debye–Hückel plus hole approximation in complex plasma

The authors analyse two‐component electroneutral systems of classical macroions of finite size and point‐like oppositely charged microions. This article deals with the modification of the Debye–Hückel plus hole approximation when a non‐linear screening effect is taken into account in a complex plasma. Parameters of non‐linear screening of the macroions by surrounding microions are calculated within the framework of the Poisson–Boltzmann approximation. Two effects are found as a result of such calculations: (a) subdivision of all microions into two subclasses, free microions and bound microions and (b) a significant reduction of an effective charge Z^* of the macroion in comparison with its true value Z due to the non‐linear screening by a thin high‐density envelope of the bound microions. We show that the value of a non‐ideal portion of an internal energy differs considerably in the case when the non‐linear screening effect is taken into account in the vicinity of the macroion.     

Effect of colloidal charge discretization in the primitive model

The effect of fixed discrete colloidal charges in the primitive model is investigated for spherical macroions. Instead of considering a central bare charge, as it is traditionally done, we distribute discrete charges randomly on the sphere. We use molecular dynamics simulations to study this effect on various properties such as overcharging, counterion distribution and diffusion. In the vicinity of the colloid surface the electrostatic potential may considerably differ from the one obtained with a central charge. In the strong Coulomb coupling, we showed that the colloidal charge discretization qualitatively influences the counterion distribution and leads to a strong colloidal charge-counterion pair association. However, we found that charge inversion still persists even if strong pair association is observed. Received 30 June 2000 and Received in final form 28 November 2000     

Cr,Mo,Ni在$lt;i$gt;α$lt;/i$gt;-Fe（C）中占位、键合性质及合金化效应的第一性原理研究

基于密度泛函理论第一性原理方法,采用广义梯度近似下的PW91泛函形式,计算了合金元素Cr,Mo,Ni固溶于α-Fe（C）的电子结构,从晶格畸变、结合能、态密度、重叠布居及差分电荷密度等计算结果出发探讨了合金元素在α-Fe（C）中占位、键合性质及其合金化效应,结果表明：Cr优先占据铁素体晶胞顶角位置,而Mo,Ni 优先占据体心位置;Cr与晶胞的结合能最大,晶胞最稳定,Ni次之,Mo最低;Cr,Mo,Ni 在晶胞中都存在金属键、共价键和微弱离子键的共同作用,成键轨道主要是Cr3d与Fe3d,Mo4d与Fe3d,Ni3d与Fe3d,C2p的交互作用形成的;Cr与晶胞原子间的键合作用强,晶胞的稳定性好,对增强钢材的机械性能帮助较大,Ni的键合作用较弱,但还是能保持晶胞的稳定性,Mo虽然键合作用强,但反键作用也非常强,使晶胞的稳定性大大降低,对钢材的机械性能危害较大. 关键词： 第一性原理 α-Fe（C）')" href="#">α-Fe（C） 键合性质 合金化效应     

Self-similarity of nonlinear screening in asymmetric complex plasmas

In this paper, two-component electroneutral systems of finite-sized macroions and oppositely charged point-like microions in the average spherical electroneutral Wigner–Seitz cell with a central macroion are studied. We investigate the self-similarity of nonlinear screening of highly charged macroions by microions in a classical asymmetrically charged complex plasma. This work is devoted to the problem of the relationship between the effective (‘visible’) charge of the macroion Z^* and its initial charge Z taking into account the effect of the nonlinear screening. It is analysed how the form of the dependence Z^*(Z) changes. The self-similarity of this dependence has been demonstrated for various characteristic system temperatures, macroion concentrations, and macroion sizes.     

Attraction of like-charged macroions in the strong-coupling limit

Like-charged macroions attract each other as a result of strong electrostatic correlations in the presence of multivalent counterions or at low temperatures. We investigate the effective electrostatic interaction between i) two like-charged rods and ii) two like-charged spheres using the recently introduced strong-coupling theory, which becomes asymptotically exact in the limit of large coupling parameter (i.e. for large counterion valency, low temperature, or high surface charge density on macroions). In contrast to previous applications of the strong-coupling theory, we deal with curved surfaces and an additional parameter, referred to as Manning parameter, is introduced, which measures the ratio between the radius of curvature of macroions to the Gouy-Chapman length. This parameter, together with the size of the confining box enclosing the two macroions and their neutralizing counterions, controls the counterion-condensation process that directly affects the effective interactions. For sufficiently large Manning parameters (weakly-curved surfaces), we find a strong long-ranged attraction between two macroions that form a closely-packed bound state with small surface-to-surface separation of the order of the counterion diameter in agreement with recent simulations results. For small Manning parameters (highly-curved surfaces), on the other hand, the equilibrium separation increases and the macroions unbind from each other as the confinement volume increases to infinity. This occurs via a continuous universal unbinding transition for two charged rods at a threshold Manning parameter of , while the transition is strongly discontinuous for spheres because of a pronounced potential barrier at intermediate distances. Unlike the cylindrical case, the attractive forces between spheres disappear slowly for increasing confinement volume due to the complete de-condensation of counterions. Scaling arguments suggest that for moderate values of coupling parameter, strong-coupling predictions remain valid for sufficiently small surface-to-surface separations.Received: 20 August 2003, Published online: 2 March 2004PACS: 87.15.-v Biomolecules: structure and physical properties - 82.70.Dd Colloids - 87.15.Nn Properties of solutions; aggregation and crystallization of macromolecules     

Cr,Mo,Ni在γ-Fe(C)中的键合性质及对相结构稳定性的影响

基于密度泛函理论第一性原理方法,采用广义梯度近似下的PW91泛函形式,计算了合金元素Cr,Mo,Ni固溶于γ-Fe(C)的电子结构,从重叠聚居数、电荷布居数、态密度、差分电荷密度及结合能等计算结果分析探讨了合金元素在γ-Fe(C)中的键合性质及对奥氏体相稳定性的影响.结果表明:Cr,Mo在奥氏体晶胞中都存在金属键、共价键和微弱的离子键的共同作用,而Ni仅有金属键和共价键作用,几乎不受离子键作用,成键轨道主要是Cr,Mo,Ni的d轨道与Fe 3d,C 2p轨道的交互作用形成的.依据合金元素对γ-Fe(C)电子结构的影响,探讨了Cr,Mo,Ni固溶后对奥氏体相稳定性的影响.     

Effect of size and charge on ordering of a highly charged concentrated macroions in suspension

An efficient fast Fourier transform method has been employed to determine correlation function [g(r*)] using the structure factor [S(Q*)] calculated with the rescaled mean spherical approximation (RMSA) and the DLVO potential. Based on this function a parametric (size and charge) study of the ordering in a highly charged and concentrated macroions (an ideal colloid) has been made. The strength of the correlation increases with the increase in the charge on macroions and it saturates after acertain value. Similarly, a critical diameter of the particle depending on the charge on it has been found at which normal feature of the ordering disappears.     

Modeling the effects of cohesive energy for single particle on the material removal in chemical mechanical polishing at atomic scale

This paper proposes a novel mathematical model for chemical mechanical polishing (CMP) based on interface solid physical and chemical theory in addition to energy equilibrium knowledge. And the effects of oxidation concentration and particle size on the material removal in CMP are investigated. It is shown that the mechanical energy and removal cohesive energy couple with the particle size, and being a cause of the non-linear size-removal rate relation. Furthermore, it also shows a nonlinear dependence of removal rate on removal cohesive energy. The model predictions are in good qualitative agreement with the published experimental data. The current study provides an important starting point for delineating the micro-removal mechanism in the CMP process at atomic scale.     

A soft-core Thomas-Fermi pseudopotential for total energy calculations

We present a modification of the “Thomas-Fermi pseudopotential” developed by Chelikowsky for the calculation of cohesive energies of solids. In the original work, the pseudopotential was singular at the origin, owing to a cusp in the pseudowavefunction. We derive here a “Thomas-Fermi pseudopotential” based on the form of pseudowavefunction introduced by Kerker, which is smooth and nonvanishing at the origin. This pseudopotential was tested in cellular calculations of the total binding energy and equilibrium cell size of bcc Na, both of which were in excellent agreement with experiment. The precision of the variationally determined charge density n(r) was checked by calculating the corresponding chemical potential μ(r), which was virtually uniform except in a small neighborhood of the origin. An LCAO parametrization of the charge density is outlined that would be appropriate for 3D problems such as a point defect.     

The Laplace transform of the MSA pair distribution functions between macroions in an ion-dipole fluid

The Laplace transform is obtained for the pair distribution function between a pair of ions, an ion and a macroion, and a pair of macroions in an ion-dipole fluid. This fluid is a simplified model of an electrolyte with a discrete model of solvent (hard spheres with embedded point dipoles). From these results, an expression for the solvation force between macroions is obtained. This result consists of the classical DLVO result plus a series of corrections.     

Macroion-induced compositional instability of binary fluid membranes

Macroion adsorption on a mixed, fluid, lipid membrane containing oppositely charged lipids induces local changes in lipid composition at the interaction zones, and gradients at their boundaries. Including these effects in the free energy of the macroion-dressed membrane we derive its spinodal equation, and show that nonideal lipid mixing can lead to (lipid-mediated) attraction between macroions and lateral phase separation in the composite membrane. The critical nonideality for this transition is substantially smaller than that of the bare lipid membrane, decreasing with macroion size and charge. That is, the lipid membrane is destabilized by macroion adsorption.     

On the cohesive energy and charge density of uranium dioxide

Self-consistent band structure calculations have been used to calculate the cohesive energy of UO₂. The computed cohesive energy was 1.641 Ry/formula unit compared with an experimental value of 1.614 Ry/formula unit. The self consistent charge density has been compared with free atom charge densities to illustrate the formation of bonding charge between the atoms.     

剪切形变下掺杂及缺陷对MoS2电子结构的影响

本文利用密度泛函理论,研究剪切形变下掺杂改性及不同类型缺陷对MoS2电子结构的影响。发现：剪切形变下,MoS2+P体系为相对最稳定的结构,掺杂改性相较于缺陷对模型稳定性影响更小;模型MoS2+P+Se中P-Mo键易形成共价键,而其中的Se-Mo键和MoS2+P-Mo-S模型中的P-Mo键,易形成离子键;掺杂使MoS2模型能隙变大,而缺陷使能隙减小,且S和Mo原子共缺陷的模型带隙为0;缺陷相较于掺杂改性模型,更能使Mo原子周围增加电荷聚集度,带隙值更低,更能影响或调控模型的电子结构。