“Ions in Aqueous Solution: From intrinsic to collective properties”
Herein, I will discuss the fundamentals of the theory of solvation and demonstrate both quantitative and qualitative difference based on the choice of the interaction potential. Using the tools of molecular simulation, we utilize both ab initio interaction potentials based in quantum mechanics and accepted classical potentials connecting to reduced models for solvation, such as Born theory, providing insight into the validity of piece-wise linear models for ion solvation. We discuss the challenges of connecting experiments that elucidate the first solvation shell via extended x-ray absorptions fine structure (EXAFS) to molecular simulation of monovalent cations. Here, we will propose new metrics and methods to correct quantum density functional theory using better estimates of the ion-water binding energy to be obtained by higher level electronic structure methods to obtain accurate single ion free energies. Additional complexities are encountered at the level of ion-pairing where differences between classical and quantum descriptions of molecular interaction suggest dramatically different solution thermodynamics. We explore the connection between the free energy of ion-pairing and collective phenomena such as clustering in addition to long-range correlations in electrolyte solutions. This work is supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES), Division of Material Sciences and Engineering. The solution model and theoretical XANES calculations were supported by the DOE, Office of Science, BES, Division of Chemical Sciences, Geosciences, and Biosciences. PNNL is a multiprogram national laboratory operated for the DOE by Battelle under contract no. DE-AC05-76RL01830.