Parametrized direct dynamics study of rate constants of H with CH4 from 250 to 2400 K

Abstract

Erratum: "Theoretical study of the non-Arrhenius temperature dependence of thermal rate constants for the H+H 2 S → H 2 + SH reaction" [J.Four implicit potential energy surfaces ͑PESs͒ with specific-reaction-parameters ͑SRP͒ are developed and tested for the reaction CH 4 ϩH→CH 3 ϩH 2 . The first is called MPW60 and is based on the modified Perdew-Wang hybrid density-functional method with the percentage of the Hartree-Fock exchange equal to 60%. The other three PESs are constructed with multi-coefficient correlation methods ͑MCCMs͒. The second is called MCOMP2-SRP, and the third is called MC-QCISD-SRP. Both of them are parametrized for this specific reaction by starting with their corresponding global parameters. The fourth is called MCG3-SRP and is based on the MCG3-CHO semiglobal parametrization with further refinement for this specific reaction. All four SRP surfaces have a classical forward barrier height of 14.8 kcal/mol, and all three MCCM SRP surfaces have a classical endoergicity of 3.3 kcal/mol. The stationary point geometries, vibrational frequencies, and zero-point-energies are reported for several standard single-level methods and MCCMs with global parameters as well as for the four new SRP surfaces. Direct dynamics calculations are carried out using variational transition state theory with multidimensional tunneling contributions on the proposed SRP surfaces. We calculate forward reaction rate constants for the title reaction from 250 to 2400 K and compare them with the latest re-analyzed experimental results over the temperature range from 348 to 1950 K. The calculated rate constants using canonical variational theory with the small-curvature tunneling approximation carried out on the MPW60, MC-QCISD-SRP, and MCG3-SRP surfaces show good agreement with the experimental results.

Applications and validations of the Minnesota density functionals

“…In contrast, the much more expensive CCSD(T) method with the same cc-pVTZ basis set augmented with diffuse s and p functions on nonhydrogenic atoms has a mean unsigned error of 1.00 kcal/mol for the same database. The M05-2X, M06-2X, and M08-HX DFAs also perform well for barrier heights, and these four DFAs are well suited to be used as implicit potential energy surfaces (PESs) for direct dynamics [176][177][178][179] studies of reaction kinetics.…”

Effects of reagent rotational excitation on the H + CHD3 → H2 + CD3 reaction: A seven dimensional time-dependent wave packet study

“…[1][2][3][4][5][6][7][8][9][10][11] Because five of the six atoms involved are hydrogens, it is an ideal candidate for high quality ab initio quantum chemistry calculations of the potential energy surface and quantum dynamics studies. Substantial efforts have been devoted on developing an accurate global potential energy surface (PES) for the system on which reliable dynamical calculations can be carried out.…”

Dynamics of the Simplest Reaction of a Carbon Atom in a Tetrahedral Environment

“…Consequently, it has been the subject of numerous experimental studies [1] exploring the kinetics and isotope effects of both the forward and reverse reactions. Recent theoretical work includes new potential energy surface calculations, [2][3][4][5][6] direct dynamics studies, [7] calculation of isotope effects, [8] and new quantum scattering methods [9] that have been reviewed by Althorpe and Clary.[10]Herein we report the first study of the nascent CD 3 products from the H + CD 4 reaction. This isotope combination was chosen for experimental reasons because this arrangement allows for the detection of all possible reaction products: CD 3 , HD and D. We also examined the CH 3 products from the H + CH 4 reaction and find that it shows very similar behavior [11] to that reported herein for the H + CD 4 reaction.…”