Variational Transition State Theory with Multidimensional Tunneling

Fernández‐Ramos, Antonio; Ellingson, Benjamin A.; Garrett, Bruce C.; Truhlar, Donald G.

doi:10.1002/9780470116449.ch3

Cited by 325 publications

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“…The most often invoked framework to interpret rate constants is Transition State Theory (TST) [15][16][17] . TST connects the experimental rate constant with the concept of activation free energy (∆F ‡ ):…”

Section: Introductionmentioning

confidence: 99%

“…All these methods overestimate the actual rates as recrossings are not taken into account and significant effort has already been invested to improve their efficiency and recover κ. One remedy is the variational TST [12][13][14][15][16] where the dynamical bottleneck of the reaction is varied to maximize κ. Another, computationally more demanding possibility is to explicitly calculate κ 2-5 .…”

Section: Introductionmentioning

confidence: 99%

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Divided Saddle Theory: A New Idea for Rate Constant Calculation

Daru

Stirling

2014

J. Chem. Theory Comput.

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We present a theory of rare events and derive an algorithm to obtain rates from postprocessing the numerical data of a free energy calculation and the corresponding committor analysis. The formalism is based on the division of the saddle region of the free energy profile of the rare event into two adjacent segments called Saddle Domains. The method is built on sampling the dynamics within these regions: auxiliary rate constants are defined for the Saddle Domains and the absolute forward and backward rates are obtained by proper reweighting. We call our approach Divided Saddle Theory (DST). An important advantage of our approach is that it requires only standard computational techniques which are available in most molecular dynamics codes. We demonstrate the potential of DST numerically on two examples: rearrangement of alanine-dipeptide (CH3CO-Ala-NHCH3) conformers and the intramolecular Cope reaction of the fluxional barbaralane molecule.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Divided Saddle Theory: A New Idea for Rate Constant Calculation

Daru

Stirling

2014

J. Chem. Theory Comput.

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“…Quantum effects on the reaction dynamics were computed semiclassically, using the small-curvature tunneling (SCT) approximation. 7 The direct dynamics calculations were carried out with GAUSSRATE 8 as the interface between Gaussian 03 9 and POLYRATE. 10 The results of our calculations are summarized in Table 1, which gives the KIEs on the breaking of the bond between C 2 and C 4 in 1.…”

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confidence: 99%

Calculations Predict a Large Inverse H/D Kinetic Isotope Effect on the Rate of Tunneling in the Ring Opening of Cyclopropylcarbinyl Radical

et al. 2009

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Tunneling rates are expected to decrease exponentially with the square root of the effective tunneling mass. 1a Therefore, on substitution of a heavier for a lighter isotope, the observation of a large kinetic isotope effect (KIE), involving a substantial decrease in rate constant, is a commonly used diagnostic for a large contribution from quantum mechanical tunneling to a reaction. 1 However, in this communication we report the results of calculations that make the opposite prediction about some of the KIEs on the ring opening of cyclopropylcarbinyl radical (1) to 3-butene-1-yl radical (2) 2 by tunneling at cryogenic temperatures. 3 Substitution of a heavier for a lighter isotope at the radical center (C 1 ) of 1 is calculated to accelerate the rate of tunneling, giving KIEs at this carbon that are inverse. Of particular note is our prediction that substitution of deuterium for both hydrogens at C 1 will lead to a nearly 3-fold increase in the rate of reaction at temperatures so low that ring opening proceeds exclusively by tunneling from the lowest vibrational level.As in our previous computational study of tunneling in the ring opening of 1 to 2, 3 we performed unrestricted electronic structure calculations with B3LYP 4 and the 6-31G(d) basis set, 5 to carry out direct dynamics calculations of the rate of this reaction. Canonical variational transition state theory (CVT) 6 was used to locate the transition structure (TS) for the ring opening of 1 to 2. Quantum effects on the reaction dynamics were computed semiclassically, using the small-curvature tunneling (SCT) approximation. 7 The direct dynamics calculations were carried out with GAUSSRATE 8 as the interface between Gaussian 03 9 and POLYRATE. 10

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“…Transition state theory (TST) [1][2][3][4][5][6] is the most widely used method for calculating rate constants of chemical reactions.…”

Section: Introductionmentioning

confidence: 99%

Symmetry numbers and chemical reaction rates

et al. 2007

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This article shows how to evaluate rotational symmetry numbers for different molecular configurations and how to apply them to transition state theory. In general, the symmetry number is given by the ratio of the reactant and transition state rotational symmetry numbers. However, special care is advised in the evaluation of symmetry numbers in the following situations: (i) if the reaction is symmetric, (ii) if reactants and/or transition states are chiral, (iii) if the reaction has multiple conformers for reactants and/or transition states and, (iv) if there is an internal rotation of part of the molecular system. All these four situations are treated systematically and analyzed in detail in the present article. We also include a large number of examples to clarify some complicated situations, and in the last section we discuss an example involving an achiral diasteroisomer.

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Variational Transition State Theory with Multidimensional Tunneling

Cited by 325 publications

References 0 publications

Divided Saddle Theory: A New Idea for Rate Constant Calculation

Divided Saddle Theory: A New Idea for Rate Constant Calculation

Calculations Predict a Large Inverse H/D Kinetic Isotope Effect on the Rate of Tunneling in the Ring Opening of Cyclopropylcarbinyl Radical

Symmetry numbers and chemical reaction rates

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