Initial state-selected scattering for the reactions H + CH4/CHD3 and F + CHD3 employing ring polymer molecular dynamics

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.

Equilibrium–nonequilibrium ring-polymer molecular dynamics for nonlinear spectroscopy

“…Here, we present an alternative RPMD approach to two-dimensional spectroscopy, which directly considers 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 [69][70][71][72][73] and employ classical response theory. We then explore its validity and limitations both theoretically and numerically.…”

Vibrational mode-specific dynamics of the F− + CH3CH2Cl multi-channel reaction

“…Mode specificity has been widely studied for atom + molecule reactions, 1–23 however, the effect of vibrational excitations is less known for ion–molecule reactions, 24–37 such as the bimolecular nucleophilic substitution (S N 2). A typical S N 2 reaction in the gas phase has a submerged transition state as well as deep pre- and post-reaction minima supporting long-lived complex formations, which may undermine the mode-specific behavior.…”

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.…”