Showing papers by "Kwang S. Kim published in 1994"

What is the global minimum energy structure of the water hexamer? The importance of nonadditive interactions

Abstract: The global minimum energy structures of the water hexamer predicted by widely used analytic water potentials are very different from each other, while the cyclic hexamer does not appear to be a low‐lying energy structure. However, high levels of ab initio calculation predict that a number of low‐lying energy conformers including the cyclic conformer are almost all isoenergetic due to the balance of two‐body and nonadditive interactions. For modeling of water potentials, we suggest that the binding energy of the dimer be between −5.0 and −4.7 kcal (mol dimer)−1, while the three‐body corrections be taken into account to a large extent.

Ab initio studies of the conformations of methylamine and ethylenediamine: interaction forces affecting the structural stability

Abstract: The structures and conformational energies of methylamine and ethylenediamine have been studied extensively with ab initio molecular orbital theory. For methylamine, there are good linear relationships among the C-N bond length, cosine of the H-C-N-H dihedral angle, and conformational energy. For ethylenediamine which has numerous multiminima, we studied the stereoelectronic effect, steric effect, intramolecular hydrogen bonding, repulsion between hydrogens, and repulsion between lone-pair electrons. The major factor determining the conformational stabilities of the multiminima is found to be the stereoelectronic effect. The partial hydrogen bonding, though weak, contributes to the structural stability so that two isoenergetic gauche conformers become the lowest energy structures