Abstract
The inclusion of nuclear quantum effects (NQEs) in molecular dynamics simulations is one of the major obstacles for an accurate modeling of molecular scattering processes involving more than a couple of atoms. An efficient method to incorporate these effects is ring polymer molecular dynamics (RPMD). Here, we extend the scope of our recently developed method based on non-equilibrium RPMD (NE-RPMD) from triatomic chemical reactions to reactions involving more atoms. We test the robustness and accuracy of the method by computing the integral cross sections for the H/F + CH4/CHD3 reactions where the methane molecule is either initially in its vibrational ground or excited state (C-H stretch). Furthermore, we analyze the extent to which NQEs are described by NE-RPMD. The method shows significant improvement over the quasiclassical trajectory approach while remaining computationally efficient.
Highlights
One of the challenges of physical chemistry is to study in detail the dynamics of chemical reactions
We show that the NE-ring polymer molecular dynamics (RPMD) simulations describe the dominant zero-point energy (ZPE) effects present in the dynamics for a wide range of collision energies
We see that non-equilibrium RPMD (NE-RPMD) only performs marginally better than quasi-classical trajectory method (QCT) for the reaction F + CHD3, where relevant tunneling effects cannot be described with NE-RPMD
Summary
One of the challenges of physical chemistry is to study in detail the dynamics of chemical reactions. The atoms are propagated with the classical equations of motion on a potential energy surface (PES) employing initial conditions that mimic quantum rotational–vibrational states This approach has successfully revealed insights into microscopic details of chemical reaction dynamics.[43–47]. H + CH4 and its isotopic variants constitute valuable benchmark hexatomic reactions for NE-RPMD Another extensively studied reaction is F + CHD3 → FH + CD3.14,33,44,45,93–102 Czakó and Bowman performed an in-depth QCT investigation of the reaction employing a PES that does not incorporate spin–orbit (SO) coupling effects.[98,101]. As such, comparing its ICS results with those of QCT and RDQD for this reaction constitutes a good test to explore the capabilities of NE-RPMD This reaction is well suited to benchmark methods capable of approximating NQEs in full-dimensional calculations, such as NE-RPMD.
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