Kinetic isotope effects and how to describe them
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Date
2017-11
Publication Type
Journal Article
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yes
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Abstract
We review several methods for computing kinetic isotope effects in chemical
reactions including semiclassical and quantum instanton theory. These methods
describe both the quantization of vibrational modes as well as tunneling and are
applied to the H + H2 and H + CH4 reactions. The absolute rate constants
computed with the semiclassical instanton method both using on-the-fly electronic
structure calculations and fitted potential-energy surfaces are also compared
directly with exact quantum dynamics results. The error inherent in the instanton
approximation is found to be relatively small and similar in magnitude to that introduced by using fitted surfaces. The kinetic isotope effect computed by the quantum
instanton is even more accurate, and although it is computationally more expensive, the efficiency can be improved by path-integral acceleration techniques. We
also test a simple approach for designing potential-energy surfaces for the example
of proton transfer in malonaldehyde. The tunneling splittings are computed, and
although they are found to deviate from experimental results, the ratio of the
splitting to that of an isotopically substituted form is in much better agreement. We
discuss the strengths and limitations of the potential-energy surface and based on our
findings suggest ways in which it can be improved.
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published
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Journal / series
Volume
4
Pages / Article No.
61501
Publisher
American Institute of Physics
Event
Edition / version
Methods
Software
Geographic location
Date collected
Date created
Subject
Kinetic isotope effect; Quantum field theory; Potential energy; Organic compounds; Reaction rate constants
Organisational unit
09602 - Richardson, Jeremy / Richardson, Jeremy
09602 - Richardson, Jeremy / Richardson, Jeremy
Notes
Funding
125760 - Molecular Ultrafast Science and Technology (MUST) (SNF)