These treatments 31,32 only explicitly considered J = 0 and invoked a separable rotation or J-shifting approximation 34–39 to predict what the J-summed results would be. 32 showed that the initially reported QM rate constants, 31 which disagreed with variational transition state theory (VTST) calculations, 33 were inaccurate because the QM dynamics treatment was paired with a harmonic treatment of the reactant partition functions (when an anharmonic treatment of the partition functions was considered the QM and earlier VTST results were in good agreement). because of the availability of literature values for comparison, in particular, due to its use in the first accurate quantum mechanical (QM) treatment 31,32 of the thermal rate constant for a reaction with more than four atoms, namely, the H + CH 4 → H 2 + CH 3 reaction. 30 The JG PES was instead chosen by Chakraborty et al.
We note that the JG PES is not the most accurate available PES most recent studies 7,14,26–29 of the eigenspectrum of CH 4 have used the more accurate T8 PES of Schwenke and Partridge.
#Rotational dynamics calculator free
We also tabulate free energies, enthalpies, entropies, and heat capacities. The FPI partition functions presented here are estimated to be converged to within a 2σ statistical uncertainty of between 0.04% and 0.07% for the given potential energy surface for temperatures in the range 300–3000 K and are the most accurately converged partition functions for a given potential energy surface for any molecule with five or more atoms. The earlier VCI calculations are found to agree well (within ∼1.5%) with the new benchmarks. These enhanced methods are applied to calculate converged partition functions by FPI methods, and these results are compared to ones obtained earlier by vibrational configuration interaction (VCI) calculations, both calculations being for the Jordan–Gilbert potential energy surface. The second is an extension of our stratification scheme to allow some strata to be defined based only on coordinate information while other strata are defined based on both the geometry and the energy of the centroid of the Feynman path. The first is the use of importance functions for dihedral angles between sets of generalized Jacobi coordinate vectors. We also present two extensions of our importance sampling and stratified sampling schemes for calculating vibrational–rotational partition functions by the FPI method. We present an improved version of our “path-by-path” enhanced same path extrapolation scheme for Feynman path integral (FPI) calculations that permits rapid convergence with discretization errors ranging from O( P −6) to O( P −12), where P is the number of path discretization points.
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