Ring-polymer molecular dynamics studies on the rate coefficient of the abstraction channel of hydrogen plus ethane,...

To accurately compute the rates of the abstraction channels of hydrogen plus ethane (Et), propane (Pr), and dimethyl ether (DME), ring-polymer molecular dynamics (RPMD) method is used in conjunction with the recently constructed local permutation invariant polynomial neural-networks potential energy surface of the parent H + CH₄ system [Q. Meng et al., J. Chem. Phys. 144, 154312 (2016)]. For H + Et, one of the H atoms in CH₄ of the parent system is replaced by a methyl group, while for the H + DME reaction, it is replaced by the methoxyl group. For the H + Pr reaction, replacing one of the H atoms in CH₄ by an ethyl group, the terminal channel is built, meanwhile the middle channel is considered through replacing two H atoms in CH₄ by two methyl groups. Since the potential energy barriers of the title reactions must differ from the H + CH₄ barrier, the corrections have to be made by computing the ratio of free-energy barriers between H + CH₄ and the title reactions at coupled cluster with a full treatment singles and doubles (where the triples contribution is calculated by perturbation theory, that is, CCSD(T)) level. Comparing the present RPMD rates with the previous theoretical and experimental results, good agreement can be found. Moreover, probable reasons for the deviation between the present RPMD rates and the previous experimental ones are discussed.