Structural and vibrational properties of solid Mg(OH)(2) and Ca(OH)(2) - performances of various hamiltonians

The layered minerals brucite Mg(OH)(2) and portlandite Ca(OH)(2) are invest igated at the ab initio quantum mechanical level, by using the periodic CRY STAL 98 program and an all-electron Gaussian-type basis set. The equilibriu m lattice parameters, lattice formation and hydration energies (with respec t to the MO + H2O - M(OH), reaction, where M = Mg, Ca) and the Raman O-H vi brational frequencies have been evaluated. The calculations have been perfo rmed at the Hartree-Fock (HF), density functional theory (DFT) and hybrid ( B3LYP) levels. As regards DFT, the local density (LDA) and generalized grad ient (GGA) approximations have been used. Excellent agreement between calcu lated and experimental lattice and hydration energies and Raman frequencies has been found with the B3LYP approximation. (C) 2001 Elsevier Science B.V . All rights reserved.