Global Potential Energy Surfaces by Compressed‐State Multistate Pair‐Density Functional Theory for Hyperthermal Collisions in the O₂+O₂ System

Abstract

Interactions between oxygen molecules play an important role in atmospheric chemistry and hypersonic flow chemistry in atmospheric entries. Recently, high‐quality ab initio potential energy surface (PES) of the quintet O4 was reported by Paukku et al. [J. Chem. Phys. 147, 034301 (2017)]. 10543 configurations were sampled and calculated at the level of MS‐CASPT2/maug‐cc‐pVTZ with scaled external correlation. The PES was fitted to a many‐body (MB) form with the many‐body part described by the permutationally invariant polynomial approach (MB‐PIP). In this work, the PIP‐Neural Network (PIP‐NN) and MB‐PIP‐NN methods were used to refit the PES based on the same data by Paukku et al. Three PESs were compared. It was found that the performances differ significantly in the O + O3 region as well as in the long‐range region. Therefore, additional 1300 points were sampled, and the efficient compressed‐state multistate pair‐density functional theory (CMS‐PDFT) was used to calculate the electronic structure of these 1300 points and 10543 points by Paukku et al. Then, a completely new quintet PES was fitted using the MB‐PIP‐NN method. Based on this PES, the quasi‐classical trajectory (QCT) approach was used to reveal all possible reaction channels for hyperthermal O2‐O2 collisions.