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 CO 3 2 -, SO 4 2 -, OH -, F -, Cl -, Br -, and NO 3 - . 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 NO 3 - and SO 4 2 - 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 CO 3 2 - > SO 4 2 - > OH - > F - > Cl - > Br - > NO 3 -, which is consistent with the observed relative ease of exchange of anions in the ion-exchange experiments employed for the synthesis of LDHs.