Ab initio studies of the water hexamer: near degenerate structures

doi:10.1016/0009-2614(91)90007-V

Chemical Physics Letters

Volume 176, Issue 1, 4 January 1991, Pages 41-45

https://doi.org/10.1016/0009-2614(91)90007-V Get rights and content

Abstract

Ab initio HF-SCF calculations have been performed on several structures of the water hexamers which are expected to have low-lying energies in the potential energy hypersurface. The SCF results with the DZP basis sets show that the hexamer with the global minimum energy has the structure of the cyclic oxygens with the S₆ symmetry. However, the energy of the hexamer with open-book-shaped oxygens is almost as low as that of the cyclic hexamer.

References (21)

R.H. Page et al.
Chem. Phys. Letters
(1984)
K.S. Kim et al.
Chem. Phys. Letters
(1986)
J.R. Reimers et al.
Chem. Phys.
(1982)
J. Detrich et al.
Chem. Phys. Letters
(1984)
M.F. Vernon et al.
J. Chem. Phys.
(1982)
D.F. Coker et al.
J. Chem. Phys.
(1985)
J.A. Odutola et al.
J. Chem. Phys.
(1980)
J.A. Odutola et al.
J. Chem. Phys.
(1988)
Z.S. Huang et al.
J. Chem. Phys.
(1988)
M.J. Frisch et al.
J. Chem. Phys.
(1986)

There are more references available in the full text version of this article.

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Ab initio studies of the water hexamer: near degenerate structures

Abstract

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