The effect of electron correlation in unraveling the hydration properties of Sc<SUP>3+</SUP> in aqueous solution: A rigid body quantummechanics/molecular mechanics simulation study

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 theorywas applied for the QMregions in the QMCFMD 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 A for the QM/MM and QMCF MD simulations, respectively. No successful ligand exchange events were observed in QM/MMMD, while four successful ligand exchanges occurred in the QMCFMD 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. (C) 2021 Elsevier B.V. All rights reserved.