Tuesday, May 7, 2019 - 3:30pm

We discuss new and ongoing work using Local Molecular Field (LMF) theory that provides a
general unified description of mixtures of charged and polar fluids as well as apolar Lennard-
Jones type (LJ) mixtures. Our initial focus is on the special case of a dilute aqueous solution of
AB solutes where the solutes may be charged or hydrophobic and the solvent W is described by
the classical SPC/E water model. There can be very interesting behavior of the AB pair
correlation function from solvent-induced effective interactions that presents difficult problems
for both simulations and theory.
The LMF theory used here introduces a general mapping that relates the structure and
thermodynamics of a nonuniform system with long-ranged Coulomb or van der Waals
interactions to that of a simpler "mimic system" with renormalized short ranged interactions
that accurately account for the averaged effects of the long-ranged interactions in the full
system of interest. We show that LMF theory can be viewed as a natural generalization of ideas
used in the classical van der Waals equation for uniform simple liquids like Ar to nonuniform
systems and general mixtures with Coulomb interactions, where even more accurate results are
found. We discuss in particular the very different behavior of the cation-anion pair
correlation function in dilute aqueous solutions of NaCl and CaCl2 and also use LMF theory to
describe the association of Argon and Fullerene solutes in water.
Possible uses of truncated water models in biomolecular simulations, leading to a “short
solvent model” which greatly reduce the overhead from long ranged Ewald sum corrections,
while still providing an accurate description of local hydrogen bond configurations poorly
described by traditional implicit solvent models will be briefly discussed.


John Weeks


University of Maryland


RH 104