Hydration properties of magnesium and calcium ions from constrained first principles molecular dynamics.
We studied the solvation structures of the divalent metal cations Mg(2+) and Ca(2+) in ambient water by applying a Car-Parrinello-based constrained molecular dynamics method. By employing the metal-water oxygen coordination number as a reaction coordinate, we could identify distinct aqua complexes characterized by structural variations of the first coordination shell. In particular, our estimated free-energy profile clearly shows that the global minimum for Mg(2+) is represented by a rather stable sixfold coordination in the octahedral arrangement, in agreement with experiments. Conversely, for Ca(2+) the free-energy curve shows several shallow local minima, suggesting that the hydration structure of Ca(2+) is highly variable. Implications for water exchange reactions are also discussed.
Ikeda
Takashi
T
Quantum Beam Science Directorate, Japan Atomic Energy Agency (JAEA), 1-1-1 Kouto, Sayo, Hyogo 679-5148, Japan.
Boero
Mauro
M
Terakura
Kiyoyuki
K
D002118:Calcium / Q000737:chemistry*; D002413:Cations, Divalent / Q000737:chemistry; D003198:Computer Simulation; D008274:Magnesium / Q000737:chemistry*; D008958:Models, Molecular; D012996:Solutions; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
D002413:Cations, Divalent; D012996:Solutions; D014867:Water; D008274:Magnesium; D002118:Calcium