Machine learning‐assisted study of correlation between post‐transition‐state bifurcation and initial phase information at the ambimodal transition state

Abstract

The Diels‐Alder cycloaddition of cyclopentadiene and nitroethene, the intramolecular cycloaddition between a diene and triene, and the Diels‐Alder cycloaddition of 2‐hydroxyacrolein with 1,3‐butadiene involving post‐transition‐state bifurcation (PTSB) were studied. These cycloaddition reactions were investigated using quasi‐classical trajectory (QCT), classical molecular dynamics (MD), ring‐polymer molecular dynamics (RPMD) simulations, and supervised machine learning binary classification techniques. Room‐temperature simulations of the ambimodal transition state (TS) using the QCT, classical MD, and RPMD methods presented similar dynamics. Binary classification revealed that the initial geometry displacement from the ambimodal TS for the Diels‐Alder cycloaddition of cyclopentadiene and nitroethene contributed to the branching dynamics and that the initial momenta for the intramolecular cycloaddition between a diene and triene and the Diels‐Alder cycloaddition of 2‐hydroxyacrolein with 1,3‐butadiene played a significant role in the bifurcation dynamics.

Molecular dynamics simulation study of post‐transition state bifurcation: A case study on the ambimodal transition state of dipolar/Diels–Alder cycloaddition

“…Thus, we can conclude that the initial momentum vectors of modes 2 and 3 in the classical dynamics significantly influence the bifurcation dynamics. It is worth mentioning that a strong correlation between the bifurcation outcome and the vibrational modes (modes 2 and 3) at the ambimodal transition state was previously observed in our previous PTSB dynamics study for the similar dipolar/Diels–Alder reaction of 1,3‐butadiene with 2‐hydroxyacrolein 36 …”

“…In this study, we conducted three types of MD calculations using QCT, classical MD, and RPMD. Since the details of our methods are provided in Murakami et al, 34–36 we offer only a brief overview here. The QCT calculations were carried out using the Born–Oppenheimer molecular dynamics (BOMD) technique implemented in the Gaussian 09 program package 33.…”

Computational study of the post-transition state dynamics for the OH + CH3OH reaction probed by photodetachment of the CH3O−(H2O) anion

“…33,34 The quantum and classical Boltzmann distribution around the equilibrium structure was achieved using path-integral molecular dynamics (PIMD) approach. Subsequently, we performed real-time propagated simulations of dissociative photodetachment dynamics on the neutral PESs from Franck–Condon region using the RPMD technique, 35–45 as well as classical MD. The paper centers its discussion on the influence of Franck–Condon overlap characteristics between the anion and neutral PESs, alongside the influence of neutral PES landscapes, on dissociation dynamics.…”

Predicting Selectivity with a Bifurcating Surface: Inaccurate Model or Inaccurate Statistics of Dynamics?

“…Typically, for ground-state reactions with large excitation gaps, Born−Oppnheimer approximation without quantum correction is usually accurate enough. 35 However, it still remains difficult to obtain a suitable statistical margin from QCT-MD trajectories for most known cases of PTSB, since collection of statistically meaningful trajectories can be computationally intensive. As a result, it is always hard to judge whether a discrepancy between the dynamic simulation and a theoretical hypothesis is from an exception to the theory where further improvement is needed or is merely due to insufficient sample size, especially for weakly selective systems.…”

“…In the former, a commonly used method is quasiclassical direct molecular dynamics, which start with initial conditions sampled from quantized vibrational mode energy. , In the latter issue, accuracy can be determined by the intrinsic accuracy of quantum chemistry calculations for the energies (and forces), the quantum effect of the nuclei, and the adiabaticity of nuclear motions. Typically, for ground-state reactions with large excitation gaps, Born–Oppnheimer approximation without quantum correction is usually accurate enough …”