Medium effects on the molecular electronic structure. I. The formulation of a theory for the estimation of a molecular electronic structure surrounded by an anisotropic medium

Electrostatic interactions play an important role in numerous self-assembly phenomena, including colloidal aggregation. Although colloids typically have a dielectric constant that differs from the surrounding solvent, the effective interactions that arise from inhomogeneous polarization charge distributions are generally neglected in theoretical and computational studies. We introduce an efficient technique to resolve polarization charges in dynamical dielectric geometries, and demonstrate that dielectric effects qualitatively alter the predicted self-assembled structures, with surprising colloidal strings arising from many-body effects.PACS numbers: 77.84. Nh, 82.70.Dd, 61.20.Ja, 77.22.Ej Colloids are ubiquitous in systems of physical, chemical, and biological interest. In suspension, dissociation of surface groups frequently causes these particles to carry an electrical charge, resulting in electrostatic interactions that play an important role in colloidal stability, aggregation, and self-assembly [1][2][3]. Far less is known about the effect of induced polarization charges. Although molecular dynamics (MD) and Monte Carlo simulations of charged colloids are now commonplace, they rarely take into account dielectric effects and instead treat the dielectric constant as spatially uniform. This is particularly striking in view of the large dielectric contrast between typical colloids and an aqueous solution (e.g., κ ≈ 2.5 for polystyrene vs. κ ≈ 80 for water at 293 K), which induces significant polarization charges at the colloidal surface. Densely packed and anisotropic arrangements of dielectric objects make this approximation even less justified. Thus, there is a pressing need to assess the role of dielectric effects in self-assembly phenomena.Proper treatment of dielectric effects has been limited by computational complexity. Only the simplest dielectric geometries permit analytical solution. For an interacting system of dielectric spheres, a series expansion has been derived [4], but this still requires expensive numerical evaluation. A more general approach is to numerically solve the induced bound charge self-consistently over discretized dielectric interfaces [5][6][7][8][9][10]. This approach does not constrain the geometry, but has not yet been efficient enough to allow simulation of dynamical dielectric objects, such as mobile colloids. Indeed, existing work has largely treated the dielectric geometry as static, focusing on ion distributions in planar [11][12][13] or spherical [14,15] geometries.In this Letter, we address this situation by presenting the first study of a dielectric system with a fully dynamic geometry, exploring the effect of polarization charges that respond to and influence the motion of charged colloids. Using an optimized simulation method [16] we explicitly demonstrate that dielectric interactions can qualitatively alter self-assembly in a prototypical size-asymmetric binary mixture of charged colloids in solution. In particular, polarization charge that binds a colloid pair ca...

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“…The strategy is to solve Eq. (6) as a discretized matrix equation for the surface charge density σ(r) [8,19],…”

Section: Potential Energymentioning

confidence: 99%

Dielectric Effects in the Self-Assembly of Binary Colloidal Aggregates

2014

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“…The electric field originated in surface charges, i.e., a reaction field, acts back on the solute. The strength of the reaction field is principally proportional to the value of the factor (E -1 ) / (~ + 1) when a given solute is surrounded by a homogeneous dielectric with dielectric constant E .42, 52 The Schrodinger equation of the solute is given as follows:…”

Section: Theoretical Aspectsmentioning

confidence: 99%

General parameterization of a reaction field theory combined with the boundary element method

Furuki¹,

Umeda²,

Sakurai³

et al. 1994

J Comput Chem

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We described various technical aspects in applying reaction field theories using continuum models to practical problems. It was investigated how solvent-dependent properties of solute molecules are influenced by the following factors: difference in quantum-chemical description of solutesolvent (continuum dielectric) interaction, difference in values of empirically determinable parameters such as atomic radii to define a size of a cavity created in a dielectric to accommodate a solute, and difference in the sophistication level of molecular orbital calculation, including electron correlation and different parameter sets (MNDO, AM1, and PM3). Through these investigations, the better parameter sets were found to evaluate accurately physicochemically important parameters such as hydration enthalpy.

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“…Various boundary element methods (BEM) in apparent surface charge (ASC) calculations were widely used to compute induced charges. 32,33 A variational formalism has been proposed by Allen et al 34 Inspired by this paper, a method called the induced charge computation (ICC) method was proposed by us 8,11 and used to study DLs 9 and ion channels 11,12,14,17 with Monte Carlo (MC) simulations. In all these studies, the ions stayed in their native dielectric; they did not cross dielectric boundaries.…”

Section: Introductionmentioning

confidence: 99%

A method for treating the passage of a charged hard sphere ion as it passes through a sharp dielectric boundary

Boda

Henderson

Eisenberg

et al. 2011

The Journal of Chemical Physics

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In the implicit solvent models of electrolytes (such as the primitive model (PM)), the ions are modeled as point charges in the centers of spheres (hard spheres in the case of the PM). The surfaces of the spheres are not polarizable which makes these models appropriate to use in computer simulations of electrolyte systems where these ions do not leave their host dielectrics. The same assumption makes them inappropriate in simulations where these ions cross dielectric boundaries because the interaction energy of the point charge with the polarization charge induced on the dielectric boundary diverges. In this paper, we propose a procedure to treat the passage of such ions through dielectric interfaces with an interpolation method. Inspired by the "bubble ion" model (in which the ion's surface is polarizable), we define a space-dependent effective dielectric coefficient, eff (r), for the ion that overlaps with the dielectric boundary. Then, we replace the "bubble ion" with a point charge that has an effective charge q/ eff (r) and remove the portion of the dielectric boundary where the ion overlaps with it. We implement the interpolation procedure using the induced charge computation method [D. Boda, D. Gillespie, W. Nonner, D. Henderson, and B. Eisenberg, Phys. Rev. E 69, 046702 (2004)]. We analyze the various energy terms using a spherical ion passing through an infinite flat dielectric boundary as an example.

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Medium effects on the molecular electronic structure. I. The formulation of a theory for the estimation of a molecular electronic structure surrounded by an anisotropic medium

Cited by 172 publications

References 37 publications

Dielectric Effects in the Self-Assembly of Binary Colloidal Aggregates

Dielectric Effects in the Self-Assembly of Binary Colloidal Aggregates

General parameterization of a reaction field theory combined with the boundary element method

A method for treating the passage of a charged hard sphere ion as it passes through a sharp dielectric boundary

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