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

This paper presents the results of quantum chemical and classical molecular dynamics (MD) simulations of the microhydration states of the Sr 2+ ion. The quantum chemical results strongly suggest a coordination number (CN) of 8 for the first hydration shell of Sr 2+ , which is in quantitative agreement with data available from X-ray absorption fine structure (XAFS) measurements. The calculated theoretical Sr O bond distance of 2.59 A is also in excellent agreement with the XAFS results (2.60 A). Classical MD simulations are conducted on various water models to predict the hydration structure of the Sr 2+ 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.