Effects of van der Waals interactions on the hydration of Hofmeister ions (Ca²⁺, K⁺, Na⁺) by ab initio molecular dynamics simulations

The van der Waals (vdW) interaction is an important physical effect in the description of liquid water. Based on the ab initio molecular dynamics simulations by including vdW interaction through the self-consistent density-dependent dispersion implementation proposed by Tkatchenko-Scheffler, we have systematically studied the influence of vdW interaction on the hydration structure of Ca²⁺, K⁺ and Na⁺ belonging to the Hofmeister series, which are of vital importance to a wide range of biological systems. Similar to liquid water, the H-bond structures of all the ion solutions are found to be significantly softened under the influence of vdW interactions. Embedded in such weakened H-bond network, the hydrophilic propensity of the ions is systematically enhanced as evidenced by the slightly increased coordination number for all three ions, which is facilitated by the increased interstitial water populations by the vdW interactions.