Hydration structure and dynamics of K+ and Ca2+ in aqueous solution: Comparison of conventional QM/MM and ONIOM-XS MD simulations

► The QM/MM and ONIOM-XS MD simulations of K+ and Ca2+ in water were performed. ► Significant differences between the QM/MM and ONIOM-XS results were observed. ► The ONIOM-XS simulations reveal the CN of 6.3 and 7.6 for K+ and Ca2+, respectively. ► The ONIOM-XS method shows its capability in predicting more reliable data.