Taming Coulomb interactions in models for ions and water

Coulomb interactions from the dipoles in water or in classical models for ionic solutions cause major problems because of their slow decay, both in formal statistical mechanical theory and in computer simulations, which use Ewald sums to treat periodic boundary conditions. We describe a new theoretical approach [1-6] which maps properties of a nonuniform system with long ranged Coulomb interactions in a given external field (arising, e.g., from charged solutes or walls) to those of a simpler ``mimic system'' with short-ranged intermolecular interactions in an effective or restructured field. The effective field accounts for the effects of the long ranged interactions through a self-consistent mean field average. We describe a new and very efficient way to solve the self-consistent equation for the effective field [7]. This provides a new view of classical electrostatics of molecular systems, since the effective field is shown to satisfy s equation, but with a Gaussian-smoothed total charge density [4,5]. Characteristic phenomena such as ion pairing or the dielectric and electrostatic properties of simple water models are quantitatively captured in the simpler mimic system. 

References:

[1] Y.-G. Chen, C. Kaur, and J. D. Weeks, J. Phys. Chem. B 108,  19874–19884 (2004).
[2] Y.-G. Chen and J. D. Weeks, Proc. Natl. Acad. Sci. USA 103,7560-7565 (2006).
[3] J. C. Rodgers, C. Kaur, Y.-G. Chen and J. D. Weeks, Phys. Rev. Lett. 97, 097801 (2006).
[4] J. M. Rodgers and J. D. Weeks, Proc. Natl. Acad. Sci. USA 105, 19136-19141 (2008).
[5] J. M. Rodgers and J. D. Weeks, J. Phys.: Condens. Matter 20, 494206 (2008).
[6] J. M. Rodgers and J. D. Weeks, J. Chem. Phys. 131, 244108 (2009).
[7] Z. Hu and J. D. Weeks, Phys. Rev. Lett. 105, 140602 (2010).