A molecular dynamics simulation study of KF and NaF ion pairs in hydrothermal fluids

Classical molecular dynamics (MD) simulations were performed to study the association of KF and NaF ion pairs in water in a wide range of temperatures (423-1273 K) and densities (0.10-0.60 g/cm(3)). The association constants (K-A) derived from the potentials of mean force (PMF) exhibit a rising tendency as temperature increases or density decreases. The association of NaF is similar to KF under most conditions but evidently larger at higher temperatures and lower densities. The radial distribution function (RDF) and coordination number (CN) reveal the characteristics of ion-water microstructures. There is significant water clustering near the K+/Na+ at high temperatures or low densities. The results indicate that fluoride ion acts as an important ligand complexing with K+/Na+ and promotes their migration and concentration in hydrothermal fluids. (C) 2020 Elsevier B.V. All rights reserved.