From microhydration to bulk hydration of Sr2+ metal ion: DFT, MP2 and molecular dynamics study

Abstract

This paper presents the results of quantum chemical and classical molecular dynamics (MD) simulations of the microhydration states of the Sr2+ ion. The quantum chemical results strongly suggest a coordination number (CN) of 8 for the first hydration shell of Sr2+, which is in quantitative agreement with data available from X-ray absorption fine structure (XAFS) measurements. The calculated theoretical SrO bond distance of 2.59Å is also in excellent agreement with the XAFS results (2.60Å). Classical MD simulations are conducted on various water models to predict the hydration structure of the Sr2+ ion. The CN is found to be in the range of 8–9 using SPC, TIP3P, and TIP4P-2005 water models, with the probability more skewed toward 8. MD–EXAFS study and coordination number analyses reveal that TIP4P-2005 is the best model potential for simulating water molecules to reproduce the experimentally observed absorption spectra and coordination numbers.