Attraction Between Like-Charged Walls: Short-Ranged Simulations Using Local Molecular Field Theory

Zhou

2009

Annu. Rev. Phys. Chem.

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443

521

Hydrophobicity manifests itself differently on large and small length scales. This review focuses on large length scale hydrophobicity, particularly on dewetting at single hydrophobic surfaces and drying in regions bounded on two or more sides by hydrophobic surfaces. We review applicable theories, simulations and experiments pertaining to large scale hydrophobicity in physical and biomoleclar systems and clarify some of the critical issues pertaining to this subject. Given space constraints, we could not review all of the significant and interesting work in this very active field.

Section: Theorymentioning

confidence: 99%

Dewetting and Hydrophobic Interaction in Physical and Biological Systems

Berne

Zhou

2009

Annu. Rev. Phys. Chem.

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443

521

“…Self-consistently solving the LMF equation in previous simulation work (29) proved relatively straightforward with a linear mixing parameter λ as V is the restructured potential determined by inserting the ρ q due to V i R into Eq. 4.…”

Section: Methodsmentioning

confidence: 99%

“…LMF theory has been applied to many different ionic systems, including charge mixtures (23,(28)(29)(30). General derivations of the approach are available in the literature (20)(21)(22).…”

Section: Lmf Theory For Electrostaticsmentioning

confidence: 99%

Interplay of local hydrogen-bonding and long-ranged dipolar forces in simulations of confined water

Rodgers

Proc. Natl. Acad. Sci. U.S.A.

2008

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145

Spherical truncations of Coulomb interactions in standard models for water permit efficient molecular simulations and can give remarkably accurate results for the structure of the uniform liquid. However, truncations are known to produce significant errors in nonuniform systems, particularly for electrostatic properties. Local molecular field (LMF) theory corrects such truncations by use of an effective or restructured electrostatic potential that accounts for effects of the remaining long-ranged interactions through a density-weighted mean field average and satisfies a modified Poisson's equation defined with a Gaussian-smoothed charge density. We apply LMF theory to 3 simple molecular systems that exhibit different aspects of the failure of a naïve application of spherical truncations-water confined between hydrophobic walls, water confined between atomically corrugated hydrophilic walls, and water confined between hydrophobic walls with an applied electric field. Spherical truncations of 1/r fail spectacularly for the final system, in particular, and LMF theory corrects the failings for all three. Further, LMF theory provides a more intuitive way to understand the balance between local hydrogen bonding and longer-ranged electrostatics in molecular simulations involving water.effective short-ranged model | spherical truncation | confinement | hydrophobic walls | electric field A n accurate and efficient treatment of Coulomb interactions in molecular simulations represents an important and ongoing challenge. Standard biomolecular simulation packages like CHARMM (1) and AMBER (2), in general, assign effective point charges to interaction sites even in neutral molecules to approximate the charge separation of the electron cloud along polar bonds. Effective point charges are also found in most standard water models such as the extended simple point charge (SPC/E) model (3) shown in Fig. 1A, and water molecules are increasingly being included explicitly in biomolecular simulations.To minimize edge effects in necessarily finite simulation cells, these simulations use periodic boundary conditions (4). Researchers have long sought to devise spherical truncations of the Coulomb 1/r potential so that the truncated potential accurately describes the strong Coulomb forces between closely spaced charges that lead to hydrogen bonding in water but then vanish quickly beyond some properly chosen cutoff radius. Then, only the minimum (closest) image of an interacting charge needs to be accounted for and fast and efficient simulations that scale linearly with system size are possible. In bulk-like systems these spherical truncation approaches can be surprisingly accurate, but standard estimates of thermodynamic properties in the bulk liquid are less satisfactory (5-12).However, it has long been established (13) that when these spherical truncations are employed in nonuniform geometries, such as near a lipid bilayer, there can be pronounced errors in structure, thermodynamics, and particularly electrostatic properties. In those ...

“…Equation (4) is identical to that for mixtures of charged species [17], and a derivation for small site-site molecular models requires only one further approximation, requiring that intramolecular correlations are well represented by the mimic system, a seemingly very reasonable requirement. The solution of equation (4) has been shown to yield accurate structure for both ionic solutions [22,29] and molecular water [21] in nonuniform systems, and a simple linear response method for solving the above equation has been derived [18], leading to fast and computationally efficient solutions of the LMF equation.…”

Section: Local Molecular Field (Lmf) Theory For Site-site Moleculesmentioning

confidence: 99%

“…• simulations using LMF theory yield correct charge density profiles for water confined between two walls [21] and for ions confined between charged plates [22], and…”

Section: Introductionmentioning

confidence: 99%

On the efficient and accurate short-ranged simulations of uniform polar molecular liquids

Rodgers

2011

Molecular Physics

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We show that spherical truncations of the 1/r interactions in models for water and acetonitrile yield very accurate results in bulk simulations for all site-site pair correlation functions as well as dipole-dipole correlation functions. This good performance in bulk simulations contrasts with the generally poor results found with the use of such truncations in nonuniform molecular systems. We argue that Local Molecular Field (LMF) theory provides a general theoretical framework that gives the necessary corrections to simple truncations in most nonuniform environments and explains the accuracy of spherical truncations in uniform environments by showing that these corrections are very small. LMF theory is derived from the exact Yvon-Born-Green (YBG) hierarchy by making physically-motivated and well-founded approximations. New and technically interesting derivations of both the YBG hierarchy and LMF theory for a variety of site-site molecular models are presented in appendices. The main paper focuses on understanding the accuracy of these spherical truncations in uniform systems both phenomenologically and quantitatively using LMF theory.a Corresponding author.