A new approach for efficient simulation of Coulomb interactions in ionic fluids

Abstract

We propose a simplified version of local molecular field (LMF) theory to treat Coulomb interactions in simulations of ionic fluids. LMF theory relies on splitting the Coulomb potential into a short-ranged part that combines with other short-ranged core interactions and is simulated explicitly. The averaged effects of the remaining long-ranged part are taken into account through a self-consistently determined effective external field. The theory contains an adjustable length parameter sigma that specifies the cut-off distance for the short-ranged interaction. This can be chosen to minimize the errors resulting from the mean-field treatment of the complementary long-ranged part. Here we suggest that in many cases an accurate approximation to the effective field can be obtained directly from the equilibrium charge density given by the Debye theory of screening, thus eliminating the need for a self-consistent treatment. In the limit sigma -> 0, this assumption reduces to the classical Debye approximation. We examine the numerical performance of this approximation for a simple model of a symmetric ionic mixture. Our results for thermodynamic and structural properties of uniform ionic mixtures agree well with similar results of Ewald simulations of the full ionic system. In addition we have used the simplified theory in a grand-canonical simulation of a nonuniform ionic mixture where an ion has been fixed at the origin. Simulations using short-ranged truncations of the Coulomb interactions alone do not satisfy the exact condition of complete screening of the fixed ion, but this condition is recovered when the effective field is taken into account. We argue that this simplified approach can also be used in the simulations of more complex nonuniform systems.

To be published in Journal of Chemical Physics

References in corpus (7)

• Electrostatics in Periodic Slab Geometries I
• Electrostatics in Periodic Slab Geometries II
• Connecting local structure to interface formation: a molecular scale van der Waals theory of nonuniform liquids
• Local molecular field theory for effective attractions between like charged objects in systems with strong Coulomb interactions
• Roles of repulsive and attractive forces in determining the structure of nonuniform liquids: generalized mean field theory
• Attraction Between Like-Charged Walls: Short-Ranged Simulations Using Local Molecular Field Theory
• The scaling behaviour of screened polyelectrolytes

Cited by in corpus (7)

• Interplay of local hydrogen-bonding and long-ranged dipolar forces in simulations of confined water
• Local molecular field theory for the treatment of electrostatics
• Simplistic Coulomb forces in molecular dynamics: Comparing the Wolf and shifted-force approximations
• Deconstructing classical water models at interfaces and in bulk
• Accurate Thermodynamics for Short-Ranged Truncations of Coulomb Interactions in Site-Site Molecular Models
• Relationship between Local Molecular Field Theory and Density Functional Theory for non-uniform liquids
• Phase Behaviors of Ionic Liquids Attributed to the Dual Ionic and Organic Nature