The importance of an accurate CH4 vibrational partition function in full dimensionality calculations of the H+CH4→H2+CH3 reaction

Bowman, Joel M.; Wang, Dunyou; Huang, Xinchuan; Huarte-Larrañaga, Fermı́n; Manthe, Uwe

doi:10.1063/1.1370944

Cited by 88 publications

(78 citation statements)

References 8 publications

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“…As a result it has long served as a benchmark for theoretical studies of atom plus polyatomic molecule reactions. 11,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] Much of this work has been concerned with determination of stationary point properties and the rate constants, although occasionally there has been work on the state-resolved dynamics. Many potential energy surfaces (PES) have been developed.…”

Section: Introductionmentioning

confidence: 99%

H + CD₄ Abstraction Reaction Dynamics: Excitation Function and Angular Distributions

Camden

Bechtel

et al. 2005

J. Phys. Chem. A

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We compare experimental photoloc measurements and quasi-classical trajectory calculations of the integral cross sections, lab-frame speed distributions, and angular distributions associated with the CD 3 products of the H + CD 4 (ν ) 0) f CD 3 + HD reaction at collision energies ranging from 0.5 to 3.0 eV. Of the potential energy surfaces (PES) we explored, the direct dynamics calculations using the B3LYP/6-31G** density functional theory PES provide the best agreement with the experimental measurements. This agreement is likely due to the better overall description that B3LYP provides for geometries well removed from the minimum energy path, even though its barrier height is low by ∼0.2 eV. In contrast to previous theoretical calculations, the angular distributions on this surface show behavior associated with a stripping mechanism, even at collision energies only ∼0.1 eV above the reaction barrier. Other potential energy surfaces, which include an analytical potential energy surface from Espinosa-García and a direct dynamics calculation based on the MSINDO semiempirical Hamiltonian, are less accurate and predict more rebound dynamics at these energies than is observed. Reparametrization of the MSINDO surface, though yielding better agreement with the experiment, is not sufficient to capture the observed dynamics. The differences between these surfaces are interpreted using an analysis of the opacity functions, where we find that the wider cone of acceptance on the B3LYP surface plays a crucial role in determining the integral cross sections and angular distributions.

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Section: Introductionmentioning

confidence: 99%

H + CD₄ Abstraction Reaction Dynamics: Excitation Function and Angular Distributions

Camden

Bechtel

et al. 2005

J. Phys. Chem. A

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“…70 However, if the energy of the vibrational ground state of the activated complex includes anharmonic effects, as in eq 3, then this should also be the case for the reactant partition function.…”

Section: Introductionmentioning

confidence: 99%

“…69 However, typically sufficiently accurate Q r (T) values can be obtained by calculating only the zero point energy exactly, employing the harmonic approximation to describe vibrational excitations, and using a classical approximation for rotational and translational motions. 69,70 This simplified scheme yields a sufficiently accurate partition function of CH 4 in the temperature range investigated in the present work, 69 and it is therefore employed here.…”

Section: Introductionmentioning

confidence: 99%

Comparison of Quantum Dynamics and Quantum Transition State Theory Estimates of the H + CH₄ Reaction Rate

et al. 2009

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Thermal rate constants are calculated for the H + CH 4 f CH 3 + H 2 reaction employing the potential energy surface of Espinosa-García (Espinosa-García, J. J. Chem. Phys. 2002, 116, 10664). Two theoretical approaches are used. First, we employ the multiconfigurational time-dependent Hartree method combined with flux correlation functions. In this way rate constants in the range 225-400 K are obtained and compared with previous results using the same theoretical method but the potential energy surface of Wu et al. (Wu, T.; Werner, H.-J.; Manthe, U. Science 2004, 306, 2227). It is found that the Espinosa-García surface results in larger rate constants. Second, a harmonic quantum transition state theory (HQTST) implementation of instanton theory is used to obtain rate constants in a temperature interval from 20 K up to the crossover temperature at 296 K. The HQTST estimates are larger than MCTDH ones by a factor of about three in the common temperature range. Comparison is also made with various tunneling corrections to transition state theory and quantum instanton theory.

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“…This is a pity, because it is still impossible to evaluate the quantum flux-side time-correlation function at t > 0 for all but the simplest systems. [7][8][9][10] A vast number of methods have been developed in an attempt to circumvent this problem. One type of method is to include quantum corrections into classical TST, 11,12 Behaviour of classical and quantum flux-side timecorrelation functions G fs (t) and C fs (t) as a function of time t. k ‡ C (β) is the classical TST rate and Zr(β) the reactant partition function.…”

Section: Introductionmentioning

confidence: 99%

Derivation of a true (t → 0+) quantum transition-state theory. I. Uniqueness and equivalence to ring-polymer molecular dynamics transition-state-theory

Hele¹,

Althorpe²

2013

The Journal of Chemical Physics

111

215

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Surprisingly, there exists a quantum flux-side time-correlation function which has a non-zero t → 0+ limit, and thus yields a rigorous quantum generalization of classical transition-state theory (TST). In this Part I of two articles, we introduce the new time-correlation function, and derive its t → 0+ limit. The new ingredient is a generalized Kubo transform which allows the flux and side dividing surfaces to be the same function of path-integral space. Choosing this common dividing surface to be a single point gives a t → 0+ limit which is identical to an expression introduced on heuristic grounds by Wigner in 1932, but which does not give positive-definite quantum statistics, causing it to fail while still in the shallow-tunnelling regime. Choosing the dividing surface to be invariant to imaginary-time translation gives, uniquely, a t → 0+ limit that gives the correct positivedefinite quantum statistics at all temperatures, and which is identical to ring-polymer molecular dynamics (RPMD) TST. We find that the RPMD-TST rate is not a strict upper bound to the exact quantum rate, but a good approximation to one if real-time coherence effects are small. Part II will show that the RPMD-TST rate is equal to the exact quantum rate in the absence of recrossing.

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The importance of an accurate CH4 vibrational partition function in full dimensionality calculations of the H+CH4→H2+CH3 reaction

Cited by 88 publications

References 8 publications

H + CD₄ Abstraction Reaction Dynamics: Excitation Function and Angular Distributions

H + CD₄ Abstraction Reaction Dynamics: Excitation Function and Angular Distributions

Comparison of Quantum Dynamics and Quantum Transition State Theory Estimates of the H + CH₄ Reaction Rate

Derivation of a true (t → 0+) quantum transition-state theory. I. Uniqueness and equivalence to ring-polymer molecular dynamics transition-state-theory

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The importance of an accurate CH4 vibrational partition function in full dimensionality calculations of the H+CH4→H2+CH3 reaction

Cited by 88 publications

References 8 publications

H + CD4 Abstraction Reaction Dynamics: Excitation Function and Angular Distributions

H + CD4 Abstraction Reaction Dynamics: Excitation Function and Angular Distributions

Comparison of Quantum Dynamics and Quantum Transition State Theory Estimates of the H + CH4 Reaction Rate

Derivation of a true (t → 0+) quantum transition-state theory. I. Uniqueness and equivalence to ring-polymer molecular dynamics transition-state-theory

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Product

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H + CD₄ Abstraction Reaction Dynamics: Excitation Function and Angular Distributions

H + CD₄ Abstraction Reaction Dynamics: Excitation Function and Angular Distributions

Comparison of Quantum Dynamics and Quantum Transition State Theory Estimates of the H + CH₄ Reaction Rate