Permutation Invariant Polynomial-neural Network Approach Research Articles

An accurate full-dimensional potential energy surface for the reaction OH + SO → H + SO2.

In this work, we report a full-dimensional accurate potential energy surface (PES-2020) for the reaction OH + SO → H + SO2, a prototype with deep complexes HOSO and HSO2. About 44 700 points are calculated at the level of UCCSD(T)-F12a/aug-cc-pVTZ and fitted by the permutation invariant polynomial-neural network (PIP-NN) approach. Particular attention is paid to the treatment of the electronic structure calculation so that the UCCSD(T)-F12a/aug-cc-pVTZ method can efficiently provide a reliable description for the ground electronic state of the title reaction. Comprehensive analyses and comparison show that the only available DMBE-PES is significantly different from the new PES-2020. Dynamics simulations on this new PES-2020 show that the reactivity decreases with the increase in collision energy. The isotropic product angular distributions remain within the studied collision energy range, 1-20 kcal mol-1, complying with the deep intermediates involved during the reaction process. The product energy partitioning is also analyzed. This accurate full-dimensional PES-2020 paves the way to fully understand the dynamics of the title reaction.

Rate coefficients and branching ratio for multi-channel hydrogen abstractions from CH3OH by F

The hydrogen abstraction reaction F+CH3OH has two possible reaction pathways: HF+CH3O and HF+CH2OH. Despite the absence of intrinsic barriers for both channels, the former has a branching ratio comparable to the latter, which is far from the statistical limit of 0.25 (one out of four available H atoms). Furthermore, the measured branching ratio of the two abstraction channels spans a large range and is not quantitatively reproduced by previous theoretical predictions based on the transition-state theory with the stationary point information calculated at the levels of Møller-Plesset perturbation theory and G2. This work reports a theoretical investigation on the kinetics and the associated branching ratio of the two competing channels of the title reaction using a quasi-classical trajectory approach on an accurate full-dimensional potential energy surface (PES) fitted by the permutation invariant polynomial-neural network approach to ca. 1.21 × 105 points calculated at the explicitly correlated (F12a) version of coupled cluster singles doubles and perturbative triples (CCSD(T)) level with the aug-cc-pVDZ basis set. The calculated room temperature rate coefficient and branching ratio of the HF+CH3O channel are in good agreement with the available experimental data. Furthermore, our theory predicts that rate coefficients have a slightly negative temperature dependence, consistent with barrierless nature of the reaction.

Dissociative chemisorption of methane on Ni(111) using a chemically accurate fifteen dimensional potential energy surface.

A fifteen-dimensional global potential energy surface for the dissociative chemisorption of methane on the rigid Ni(111) surface is developed by a high fidelity fit of ∼200 000 DFT energy points computed using a specific reaction parameter density functional designed to reproduce experimental data. The permutation symmetry and surface periodicity are rigorously enforced using the permutation invariant polynomial-neural network approach. The fitting accuracy of the potential energy surface is thoroughly investigated by examining both static and dynamical attributes of CHD3 dissociation on the frozen surface. This potential energy surface is expected to be chemically accurate as after correction for surface temperature effects it reproduces the measured initial sticking probabilities of CHD3 on Ni(111) for various incidence conditions.

Ring polymer molecular dynamics fast computation of rate coefficients on accurate potential energy surfaces in local configuration space: Application to the abstraction of hydrogen from methane.

To fast and accurately compute rate coefficients of the H/D + CH4 → H2/HD + CH3reactions, we propose a segmented strategy for fitting suitable potential energy surface (PES), on which ring-polymer molecular dynamics (RPMD) simulations are performed. On the basis of recently developed permutation invariant polynomial neural-network approach [J. Li et al., J. Chem. Phys. 142, 204302 (2015)], PESs in local configuration spaces are constructed. In this strategy, global PES is divided into three parts, including asymptotic, intermediate, and interaction parts, along the reaction coordinate. Since less fitting parameters are involved in the local PESs, the computational efficiency for operating the PES routine is largely enhanced by a factor of ∼20, comparing with that for global PES. On interaction part, the RPMD computational time for the transmission coefficient can be further efficiently reduced by cutting off the redundant part of the child trajectories. For H + CH4, good agreements among the present RPMD rates and those from previous simulations as well as experimental results are found. For D + CH4, on the other hand, qualitative agreement between present RPMD and experimental results is predicted.

Communication: An accurate full 15 dimensional permutationally invariant potential energy surface for the OH + CH4 → H2O + CH3 reaction.

A globally accurate full-dimensional potential energy surface (PES) for the OH + CH4 → H2O + CH3 reaction is developed using the permutation invariant polynomial-neural network approach based on ∼135,000 points at the level of correlated coupled cluster singles, doubles, and perturbative triples level with the augmented correlation consistent polarized valence triple-zeta basis set. The total root mean square fitting error is only 3.9 meV or 0.09 kcal/mol. This PES is shown to reproduce energies, geometries, and harmonic frequencies of stationary points along the reaction path. Kinetic and dynamical calculations on the PES indicated a good agreement with the available experimental data.