Strong Attractions and Repulsions Mediated by Monovalent Salts Supporting Information Appendix

The ion-ion radial distribution functions used in the Iterative Boltzmann Inversion (see main text and the section 2 of this SI Appendix) are calculated from atomistic simulations of NaCl-water solutions. Periodic boundary conditions (PBC) are applied on the x-, yand zdimensions of a 5 nm × 5 nm × 5 nm simulation box. NaCl concentrations from 0.3 M to 1 M are simulated. The number of water molecules in the simulation box range from 4131 to 3575 depending on NaCl concentration. Particle Mesh Ewald (PME) method (1) is applied to treat the electrostatic interaction beyond the cutoff of 1.2 nm. The simulation timestep is 1 fs. The systems are equilibrated at a constant pressure of 1 atm for 5 ns before collecting data. Two water models are studied: the TIP3P model and SPC/E model. The systems with TIP3P water model are simulated using NAMD (2) which is optimized for TIP3P water model, and the systems with SPC/E are simulated using GROMACS (3).