The 1-D hindered rotor approximation |
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Authors: | Jim Pfaendtner Xinrui Yu Linda J Broadbelt |
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Institution: | (1) Department of Chemical and Biological Engineering, Northwestern University, Evanston, IL 60208-3120, USA |
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Abstract: | We offer an overview of the popular one- dimensional (1-D) hindered rotor model that is often used for quantum mechanical
treatment of internal rotation. This model is put in context with other methods used for treating anharmonic motions. The
1-D hindered rotor scheme is general for tops of any symmetry and has been used to provide accurate treatment of hindered
rotors in a wide range of systems. One obstacle preventing wider use of the model is its lack of incorporation into common
electronic structure codes. We have developed an algorithm for consistently treating all tops in a molecule, and we present
simple codes which interface with electronic structure codes to provide thermochemical properties (S, C
p
, H) of individual species and reactions that have been corrected for internal rotations. Finally, we use this approach to
give sensible advice about how the model can be used best. We show that dramatic changes in the reduced moment of inertia
do not necessarily cause comparable changes in the properties of individual hindered rotors. We demonstrate that the rotational
hindrance potential can be accurately determined using relatively coarse step sizes. Finally, we show that internal rotation
in transition states can be treated using a “frozen transition state” approximation at a significant computational savings.
We also discuss the relationship between calculated properties of hindered rotors and the choice of method and basis set used.
Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
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