Nuclear quantum effects in state-selective scattering from ring polymer molecular dynamics

Abstract

We present an efficient method to obtain initial state-selective cross sections for bimolecular reactions that can account for certain nuclear quantum effects by employing the ring polymer molecular dynamics approach. The method combines the well known quasiclassical trajectory (QCT) approach with the description of the system in an extended ring polymer phase space. Employing the prototypical Mu/H/D + H 2 (v = 0, 1) reactions as a benchmark, we show that the presented approach does not violate zero-point energy constraints and that it can also capture the contributions of tunneling through the v = 1 vibrationally adiabatic barrier present for the Mu + H 2 (v = 1) reaction. This is a significant improvement over the QCT approach with only a small increase in numerical cost.

State‐selective cross sections from ring polymer molecular dynamics

“…These systems were studied in our previous work, which dealt with the ICSs for the corresponding systems around their thresholds. [ 83 ] Here, we recomputed the ICSs with a different β , that is, with the previous smooth energy‐dependent cut‐off instead of the abrupt β − = 300 cut‐off, as well as a wider range of collision energies. First, we focus on the reactivity of H/D with H 2 in its vibrational ground state.…”

“…This is the ansatz we used in our previous work (with and β − = 300). [ 83 ] Inducing a lower cut‐off for β is necessary for high collision energies. In our previous work, β − was chosen to a fixed value so that the extra thermal energy contributions remained within 1% of the ZPE of H 2 .…”

“…[ 82,62 ] We have proposed an efficient approach that combines the RPMD approach with QCT simulations to obtain initial state‐selective cross sections for bimolecular reactions. [ 83 ] Initial state‐selective cross sections for the Mu/H/D + H 2 ( ν = 0,1) reactions were calculated close to the threshold energy. It was shown that the approach approximately incorporates ZPE constraints and includes some tunneling contributions.…”

Path-integral approximations to quantum dynamics

“…This has been exploited recently with the development of nonequilibrium RPMD [133] (following earlier explorations of non-equilibrium CMD [134,135]), which has had interesting recent applications to hydrogen-graphene scattering [136,137], gas-surface reactions [138], and to excited-state dynamics [139]. Closely related to this are the recent developments of microcanonical RPMD [140][141][142].…”

Equilibrium-nonequilibrium ring-polymer molecular dynamics for nonlinear spectroscopy

“…Here, we present an alternative RPMD approach to two-dimensional spectroscopy, which directly approximates the two-time response function and does not rely on the additional approximation related to the DKT correlation function. To derive the proposed method, we start from the recently developed nonequilibrium RPMD [51][52][53][54][55] and employ classical response theory. We then explore its validity and limitations both theoretically and numerically.…”