Interactions in aqueous salt solutions: Atomistic modelling versus experiment

The research in this thesis investigates how atoms and molecules constituting aqueous salt solutions interact using computational approaches, namely Monte Carlo simulations and molecular dynamics simulations.

In the first paper, an atomistic model was developed for aqueous solutions of sodium thiocyanate and potassium thiocyanate (NaSCN and KSCN). The model reproduced several experimentally measured thermodynamic properties in bulk solution and at the air-water interface. The model further gave insight into cation specific effects on the thiocyanate anion. K⁺ was found to show a preferential attraction to the S atom of SCN^-, forming a diffuse first coordination shell around the atom. Na⁺, on the other hand, showed a relatively stronger preferential interaction with the N atom of SCN^-  resulting in a more distinct first coordination shell. At high salt concentration, the difference in cation-anion interactions resulted in NaSCN forming larger and more closely packed clusters than KSCN.

In the second paper, a method handling long-range electrostatic interactions was developed, using a short-ranged potential. The method is mathematically exact and has physical foundation in that it cancels an arbitrary number of electrostatic moments at the cutoff. With an appropriate choice of how many moments that are cancelled, the method was shown to produce accurate results compared to Ewald and particle mesh Ewald. The method is advantageous in that it scales with Ο(N), compared with Ewald and particle mesh Ewald, scaling with Ο(N^3/2) and O(Nlog(N)), respectively.