Molecular Dynamics Modeling of the Structures and Binding Energies of α-Nickel Hydroxides and Nickel−Aluminum Layered Double Hydroxides Containing Various Interlayer Guest Anions

Molecular dynamics (MD) simulations of β-Ni(OH)2, α-Ni(OH)2, and Ni/Al-layered double hydroxides (LDHs) have been performed in order to study structures and binding energies of the materials containing various anions such as CO32-, SO42-, OH-, F-, Cl-, Br-, and NO3-. We propose a modified force field of the cff91 form with the introduction of a double-well potential for describing oxygen−metal−oxygen angle bending. New parameters for describing the Ni−O bond and some refined nonbond parameters are suggested. The structural parameters of β-Ni(OH)2, α-Ni(OH)2, and Ni/Al-LDHs obtained with the modified force field are in good agreement with experimental values. For NO3- and SO42- contained LDHs, the simulated results suggest several possible stacking modes of interlayer anions and water molecules. The stability of dehydrated β-Ni(OH)2 has also been rationalized by the hydration energy of β-Ni(OH)2. The relative binding energies of interlayer anions in α-Ni(OH)2 and Ni/Al-LDHs decrease in the order CO32- > SO42- > OH- > F- > Cl- > Br- > NO3-, which is consistent with the observed relative ease of exchange of anions in the ion-exchange experiments employed for the synthesis of LDHs.