Title: Double layer for hard spheres with an off-center charge
Author(s):

	W. Silvestre-Alcantara (Department of Physics and Laboratory for Theoretical Physics, University of Puerto Rico, San Juan, Puerto Rico 00936-8377, USA) ,
	L.B. Bhuiyan (Department of Physics and Laboratory for Theoretical Physics, University of Puerto Rico, San Juan, Puerto Rico 00936-8377, USA) ,
	S. Lamperski (Department of Physical Chemistry, Adam Mickiewicz University in Poznan, Umultowska 89b, 61-614 Poznan, Poland) ,
	M. Kaja (Department of Physical Chemistry, Adam Mickiewicz University in Poznan, Umultowska 89b, 61-614 Poznan, Poland) ,
	D. Henderson (Department of Chemistry and Biochemistry, Brigham Young University, Provo UT 84602-5700)

Simulations for the density and potential profiles of the ions in the planar electrical double layer of a model electrolyte or an ionic liquid are reported. The ions of a real electrolyte or an ionic liquid are usually not spheres; in ionic liquids, the cations are molecular ions. In the past, this asymmetry has been modelled by considering spheres that are asymmetric in size and/or valence (viz., the primitive model) or by dimer cations that are formed by tangentially touching spheres. In this paper we consider spherical ions that are asymmetric in size and mimic the asymmetrical shape through an off-center charge that is located away from the center of the cation spheres, while the anion charge is at the center of anion spheres. The various singlet density and potential profiles are compared to (i) the dimer situation, that is, the constituent spheres of the dimer cation are tangentially tethered, and (ii) the standard primitive model. The results reveal the double layer structure to be substantially impacted especially when the cation is the counterion. As well as being of intrinsic interest, this off-center charge model may be useful for theories that consider spherical models and introduce the off-center charge as a perturbation.

Key words: electrical double layer, simulations, density functional theory, off-center charged spheres
PACS: 61.20.Qj, 82.45.Fk, 82.45.Gj, 82.45.Jn

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