The structural equilibrium parameters, the formation and hydration energies, and the O-H vibrational frequencies of LiOH and NaOH have been investigated at the ab initio level by using the periodic CRYSTAL package. Four different methods have been adopted for comparison. The computed structural parameters are in good agreement with experiment. Computational results Lire all in excellent agreement with experiment, except for the heat of hydration of LiOH, which was found to be overestimated with respect to experiment. The OH group in the two cases does not present any hydrogen bond type interaction. Among the four methods, B3LYP gives the best results for all the features considered, in particular for the OH(D) vibrational data. (C) 2004 Elsevier B.V. All rights reserved.