The role of second shell quantum effects on the preferential solvation of Li+ in aqueous ammonia: An extended ab initio QM/MM MD simulation with enlarged QM region

The preferential Li+ solvation in aqueous ammonia has been revisited by performing an extended ab initio QM/MM MD simulation, in which the QM region’s size was enlarged to 4.2 Å radius. The use of larger QM region leads to a clear water preference with an arrangement of Li+[(H2O)4][(H2O)4] type, compared to the preferred Li+[(H2O)3NH3][(H2O)4(NH3)2] structure obtained by a previous QM/MM simulation using a small QM region not comprising the second solvation shell. The observed discrepancies clearly demonstrate the importance of quantum chemical treatment of the second shell in order to obtain a reliable and accurate description of this solvated ion.