The effect of electron correlation in unraveling the hydration properties of Sc3+ in aqueous solution: A rigid body quantum mechanics/molecular mechanics simulation study

Abstract

The structural and dynamical properties of Sc3+ have been studied using quantum mechanics/molecular mechanics (QM/MM) and quantum mechanical charge field (QMCF) MD simulations. The QM region in the QM/MM MD simulation is treated using the resolution-of-identity MP2 level of theory, whereas the Hartree–Fock (HF) level of theory was applied for the QM regions in the QMCF MD simulation. Based on these two approaches, Sc3+ is hydrated by six water molecules in the first hydration shell. The average bond distances of Sc3+ − water are 2.15 and 2.16 Å for the QM/MM and QMCF MD simulations, respectively. No successful ligand exchange events were observed in QM/MM MD, while four successful ligand exchanges occurred in the QMCF MD simulation. These results proved the rigidity of the first hydration shell of Sc3+. In comparison with the other rare earth elements, Sc3+ showed the strongest interaction with water as reflected in the 214.76 and 192.52 N/m force constant values for the QM/MM and QMCF MD simulations, respectively. Electron correlation plays a role in strengthening the interactions between Sc3+ and water molecules in the first hydration shell.