AN EXTENDED BASIS-SET AB-INITIO STUDY OF ALKALI-METAL CATION-WATER CLUSTERS

Ionic clusters comprised of a single alkali metal cation and up to eig ht water molecules were studied at the Hartree-Fock and correlated lev els of theory using the correlation consistent sequence of basis sets. Estimates of the degree of convergence in the computed properties wit h respect to the complete basis set limit were facilitated by the unde rlying systematic manner in which the correlation consistent sets appr oach completeness. In favorable cases, improved property values could be obtained by fitting finite basis set results with a simple analytic al expression in order to extrapolate to the complete basis set limit. The sensitivity of structures and binding energies were analyzed with regard to the inclusion of valence and core-valence correlation recov ery at the MP2, MP4, and CCSD(T) levels of theory. The replacement of metal core electrons and the introduction of relativistic contribution s via effective core potentials was compared to corresponding all-elec tron results. (C) 1995 American Institute of Physics.