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Isomers of C 20 : An energy profile III
Author(s) -
Chavez Jennifer I.,
Carrillo Maira M.,
Beran Kyle A.
Publication year - 2004
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.10391
Subject(s) - cartesian coordinate system , saddle point , potential energy surface , chemistry , ring (chemistry) , structural isomer , potential energy , energy profile , kinetic energy , computational chemistry , polar , geometry , energy (signal processing) , crystallography , atomic physics , stereochemistry , physics , molecule , mathematics , quantum mechanics , organic chemistry
Semiempirical calculations, at the PM3 level provided within the Winmopac v2.0 software package, are used to geometrically optimize and determine the absolute energies (heats of formation) of a variety of C 20 isomers that are predicted to exist in and around the ring and cage isomers. Using the optimized Cartesian coordinates for the ring and the cage isomers, a saddle‐point calculation was performed. The resulting energy profile, consisting of a series of peaks and valleys, is used as a starting point for the identification and location of fifteen additional isomers of C 20 that are predicted to be energetically stable, both via geometry optimizations and force constant analysis. These additional isomers were subsequently determined to lie adjacent to one another on the potential surface and establish a step‐wise transformation between the ring and the cage. Transition‐state optimization of the Cartesian coordinates at the saddle point between adjacent isomers was performed to quantify the energy of the transition state. The step‐wise process from one isomer to another, which extends out over the three‐dimensional surface, is predicted to require ∼15% less energy than that of the direct, two‐dimensional transformation predicted in the bowl‐cage profile. However, the net atomic rearrangement for the step‐wise process is about four times greater than that of the direct process. Although less in energy, the amount of atomic rearrangement in the step‐wise process would make the occurrence of such a route prohibitive. Utilizing the direct distance separating the three primary isomers (ring, bowl, cage), the method of triangulation is performed to quantitatively position other C 20 structures on the potential surface, relative to the ring, bowl, and cage isomers. © 2003 Wiley Periodicals, Inc. J Comput Chem 25: 322–327, 2004