Investigation of ions hydration using molecular modeling

Abstract

Ion hydration phenomena are of great interest in the fields of physics, chemistry, biology, geochemistry and environment. However, few studies using identical calculation methods to characterize the hydration properties of ions in water and in electrolytic systems are available. Hence, it is difficult to compare the hydration properties of ions when they come from different methods. The objective of this work is, therefore, to use a unique approach to compare the hydration properties of ions in pure water and in presence of counter-ion using a quantum mechanical method, the Density Functional Theory (DFT). For this purpose, a methodology based on the decomposition of the system's energy is described and implemented in this study. In the first part, quantum mechanics calculations are used to determine the hydration properties of ions, without counter-ion, in presence of water molecules. In the second part, the hydration characteristics of solutes in systems containing ions, counter-ions and water molecules are studied. Results show that the presence of an anion (Cl− or SO42−) does not cause structural and energetic changes in the cation first hydration layer (Li+, Na+, K+, Mg2+, Ca2+). Conversely, the anion first hydration layer depends on the cation of the system.