The O-H(D) stretching potentials of the hydrogen bonded water molecules inMCl2 center dot 2H(2)O (M is an element of {Mn, Co, Fe}). Ab initio and density functional study

The uncoupled anharmonic O-H(D) stretching vibrations of the hydrogen bonde d water molecules with local C? symmetry in compounds of the type MCl(2)(.) 2H(2)O (where M is an element of {Mn, Co, Fe}) were studied at various leve ls of theory, within the finite-cluster approach. The studied clusters cons isted of one water molecule coordinated to the metal atom and hydrogen bond ed to two chloride anions. The vibrational potential energy curves for the uncoupled OH stretching vibrations were obtained from pointwise energy calc ulations at HF, MP2 and gradient-corrected B3-LYP density functional levels of theory. To solve the HF or the Kohn-Sham equations, the standard 6-311G (d,p) basis set was used on O, H and Cl, while the transition metal atoms w ere treated within the LANL2DZ basis, employing an effective core potential (ECP) description of the inner shell electrons. From the calculated energi es of the vibrational eigenstates, both the fundamental anharmonic and harm onic vibrational Frequencies, as well as the anharmonicity constants were c omputed. (C) 2001 Elsevier Science B.V. All rights reserved.