This workshop is aimed at recent developments in the theory and modeling of ions in solutions of biological interest. The focus will be on fundamental studies of the structure and thermodynamics of realistic models, including molecules and ions in water. These solutions are important in a wide range of biophysical problems, including specific
ion effects in biology, ion channels, membranes, protein folding, and in multi-scale modeling beginning from a chemical level and building to the level of functional biomolecular structures.

Ionic interactions with the surrounding medium are exceptionally strong at short range, often competing with classic chemical bonding. Ionic interactions with the surrounding medium and with other ions are also
exceptionally long-ranged. So systems in which ions play an essential role are outstanding candidates for multi-scale modeling and theories that permit controlled and understood coarse-graining. Though standard
methods are not available, there is much current interest in
breaking through these important challenges.

Recent years have seen a rapid growth in new theoretical approaches for molecular liquids. These developments have included quasi-chemical theory and other free-energy approaches. Quasi-chemical theory partitions the solvation free energy into inner-shell and outer-shell (packing and long-ranged) components by inserting a hard-sphere
condition. Analysis of the various free energy components can yield significant insights into the mechanism of solvation. The study of occupancy statistics in the inner-shell region produces helpful information on ion selectivity. Other new free energy methods have been
developed for larger molecular solutes, and for interactions of those solutes with bio-molecules.

One general theme will be the development of new, accurate methods for examining the local solvation structure and thermodynamics of hydration. Recent work has shown that a subject as basic as the solvation
environment of simple ions is far from resolved. Thus methods which incorporate quantum mechanical sampling coupled with free energy computations will be emphasized. The development of classical polarizable force fields which can accurately represent the local solute environment will also be discussed. A major aim will be relating the
models and theories to experimental results.

Another general theme will be working toward organized inclusion of multi-ion interactions/correlations. The MacMillan-Mayer solution theory is the standard conceptual organization of this problem, but it is scarcely operational as a practical matter. Whether recent advances associated
with quasi-chemical theory might change that status is a question worth intensive examination.

The workshop will include experts in fundamental studies of molecular and ionic hydration, and individuals developing new theories and computational methods for free energy calculations.