Study of the structure of molecular complexes. IX. The Hartreendash;Fock energy surface for the H2Ondash;Lindash;F complex

摘要

A large number of geometrical configurations (250) are computed with a large Gaussian basis set in the Hartreendash;Fock approximation for the H2Ondash;Lindash;F complex. The manyhyphen;dimensional potential energy surface has been sampled by keeping the molecule of water at a fixed position and by allowing the lithium and the fluorine to assume many positions in space. Because of the symmetry (C2v) of the water molecule, the 250 computations correspond to a sampling of about 600 configurations. The sampling includes a few highly repulsive configurations (up to about 300 kcal/mole in repulsion); the remaining points are either in the strongly attractive regions or in the weakly attractive regions of the surface. The stabilization energy of the complex reveals the existence of at least three possible structures: the Lindash;Fndash;H2O structure (withC2vsymmetry), with a stabilization energy (relative to H2O, Fminus;, and Li+) of about minus;186 kcal/mole; a second Lindash;Fndash;H2O structure with the fluorine forming a hydrogen bond (with one of the Hndash;O groups of the water molecule), with a stabilization energy of about minus;191 kcal/mole; and a third structure, H2Ondash;Lindash;F (withC2vsymmetry), with a stabilization energy of about minus;201 kcal/mole. The main goal of this work is not the determination of the structures of the H2Ondash;Lindash;F complex, but the construction of a reliable potential to be used in the study of the structure and properties of ionic solutions. For this reason, the computed Hartreendash;Fock energies have been accurately fitted with a simple analytical expression. In addition, the Hartreendash;Fock energy for the complex has been analyzed by partitioning it into twohyphen;body interaction energies (Lindash;F, Li+ndash;H2O, and Fminus;ndash;H2O) and into threehyphen;body potentialhyphen;energy terms. Finally, a second type of partitioning, the sohyphen;called bond energy analysis, has been presented and discussed.