Impact of sulfate salts on water structure: insights from molecular dynamics.

Ions significantly alter the water's structure, impacting properties such as the temperature of maximum density and the freezing point. We study structural changes in water upon adding sulfate anions, specifically $ {\rm Na}_2{\rm SO}_4 $ Na 2 SO 4 , $ {\rm K}_2{\rm SO}_4 $ K 2 SO 4 , $ {\rm Li}_2{\rm SO}_4 $ Li 2 SO 4 , and $ {\rm Mg}{\rm SO}_4 $ Mg SO 4 , using computer simulations. We employ the TIP4P/2005 water and the Madrid-2019 force field. By simulating solutions at various concentrations (0.64, 1.30, 1.90, and 3 mol kg $ ^{-1} $ − 1 ) and two temperatures (300 and 240 K), we explore how these electrolytes disrupt water's structure and how they modify the interplay between Low Density Water and High Density Water. Increased salt concentration perturbed water's radial distribution functions (RDFs), particularly up to 240 K. $ {\rm Na}_2{\rm SO}_4 $ Na 2 SO 4 significantly disrupted water structure, reducing RDF peak heights and indicating decreased tetrahedrality, while $ {\rm Mg}{\rm SO}_4 $ Mg SO 4 increased structural order. $ {\rm K}_2{\rm SO}_4 $ K 2 SO 4 displayed anomalous behaviour, minimally affecting water at 1.90 mol kg $ ^{-1} $ − 1 and ambient temperature but causing more ordered structures at 240 K. Orientational order parameter $ q_t $ q t analysis supported these findings. Hydrogen bond network analysis showed notable perturbations at lower temperatures. Diffusion coefficients generally decreased with concentration, with $ {\rm K}_2{\rm SO}_4 $ K 2 SO 4 exhibiting increase at 240 K. These results highlight the complex interactions between sulfate ions and water, enhancing our understanding of electrolyte solutions. [ABSTRACT FROM AUTHOR]