Structure and dynamics of the Th4+-ion in aqueous solution – An ab initio QMCF-MD study

An ab initio quantum mechanical charge-field molecular dynamics simulation of the tetravalent thorium ion in aqueous environment is presented. Including the first and second hydration shell in the quantum mechanical treatment to enhance accuracy, this study yields very good results for a wide range of characteristics, as compared to experimental data. 20 ps of simulation time were used to investigate structural and dynamical properties of the hydrate by numerous methods, including radial and angular distribution functions, three-body distribution functions, ligand exchange analysis and vibrational spectra. The hydrate proved stable during the simulation and did not show hydrolysis. The first solvation shell was found to be a very flexible one, with a number of intrashell ligand rearrangements occurring along the simulation. The data of the simulation also indicated the existence of a third hydration layer. Vibrational analysis yielded an average ion–oxygen frequency of 420 cm−1, which is in excellent agreement with experimental data.