Before revision:  We discover that the atom radius of Ca2+ in conventional force fields is too large for the QM calculation to capture the variation in  coordination geometry of Ca2+ in its ionic form and lead to unphysical charges.
After revision:  We discover that the atom radius of Ca2+ in conventional force fields is too large for the QM calculation to capture the variation in coordination geometry of Ca2+ in its ionic form , leading to unphysical charges.