Accurate Full-Dimensional Global Diabatic Potential Energy Matrix for the Two Lowest-Lying Electronic States of the H + O₂ ↔ HO + O Reaction

Abstract

A new and more accurate diabatic potential energy matrix (DPEM) is developed for the two lowest-lying electronic states of HO 2 , covering both the strong interaction region and reaction asymptotes. The ab initio calculations were performed at the Davidson corrected multireference configuration interaction level with the augmented correlation-consistent polarized valence quintuple-zeta basis set (MRCI +Q/AV5Z). The accuracy of the electronic structure calculations is validated by excellent agreement with the experimental HO 2 equilibrium geometry, fundamental vibrational frequencies, and H + O 2 ↔ OH + O reaction energy. Through the combination of an electronic angular momentum-method and a configuration interaction vector-based method, the mixing angle between the first two 2 A″ states of HO 2 was successfully determined. Elements of the 2×2 DPEM were fit to neural networks with a proper account of the complete nuclear permutation inversion symmetry of HO 2 . The DPEM correctly predicted the properties of conical intersection seams at linear and T-shape geometries, thus providing a reliable platform for studying both the spectroscopy of HO 2 and the nonadiabatic dynamics for the H + O 2 ↔ OH + O reaction.

New accurate diabatic potential energy surfaces for the two lowest 1A′′ states of H2S and photodissociation dynamics in its first absorption band

“…The analytical representations of the quasi-diabatic energies and their couplings were separately fitted using the PIP-NN 38–42 scheme, which has demonstrated high flexibility and has achieved great success in representing the PESs of gas phase and gas-surface scattering processes. 38–42,59 Similar to the studies of HO 2 54 and H 2 O 42 molecules, the complete nuclear permutation and inversion (CNPI) group for H 2 S is isomorphic to the C 2v point group, where the two diabatic states belong to A 2 and B 1 irreducible representations in all configuration space. The two diagonal elements V A and V B , having the totally symmetric irreducible representation (A 2 × A 2 = B 1 × B 1 = A 1 ), are invariant under exchange of the two identical H atoms, which can be directly fitted using the PIP-NN method.…”

“…It should be noted that the quasi-diabatic representation for the polyatomic system is not unique, because the derivative coupling cannot be removed completely. 53,54 In this work, the mixing angle α was evaluated using the configuration interaction vector method proposed by Werner et al 12,55 as implemented in the MOLPRO package, where both molecular orbitals and CI vectors of the electronic wavefunctions change as little as possible relative to the reference geometry in C 2v symmetry. The diabatic potential energies and their couplings can be calculated from the adiabatic potential energies and mixing angle using the following expression:Here, the V a i are the corresponding adiabatic PESs of 1 1 A′′ and 2 1 A′′ excited states.…”

“…This diabatization method has also been successfully adapted to construct quasi-diabatic PESs for several other systems, such as F + H 2 , 56 NO 2 , 57 SO 2 , 58 and HO 2 . 54 Then the diabatic transition dipole moments can be obtained by a similar transformation:where μ a i ( i = 1, 2) are the adiabatic transition dipole moments calculated at the icMRCI-F12 + Q level, d̂ is the dipole operator, ϕ gr is the ground state wave function, and ϕ d A/B is the wave function of the A/B quasi-diabatic state. In this work, the calculated diabatic transition dipole for μ d B is symmetrical with respect to the exchange of the two H atoms as shown in Fig.…”

Quantum simulation of conical intersections

“…The process of converting the original adiabatic electronic structure data to a diabatic representation, referred as diabatization, is an active yet non-unified field due to the non-uniqueness of quasi-diabatic representations. 27–41 Third, the dynamics of nonadiabatic systems typically require a more complex treatment than the dynamics on a single potential energy surface. For example, we need to expand wavefunctions in the basis of every diabatic state to account for effective state transition in quantum dynamics.…”

Impact of Geometric Phase on Dynamics of Complex-Forming Reactions: H + O2 → OH + O

“…Unfortunately, rigorous diabatization is not possible for systems with more than two atoms, , but the residual derivative coupling can be minimized in a so-called quasi-diabatic representation . Diabatization is the determination of the unitary adiabatic-to-diabatic (AtD) transformation that converts the diagonal adiabatic PESs into a diabatic potential energy matrix (DPEM), in which the diagonal and off-diagonal elements are all smooth functions of the nuclear coordinates, thus amenable to analytical representation. , Recently, we developed a two-state DPEM for the title reaction at the multireference configuration interaction with Davidson correction (MRCI+Q) level with a large basis set . This machine-learned high-fidelity DPEM based on ab initio data is expected to be more accurate than the existing one based on the diatom-in-molecule (DIM) form, thus providing a reliable platform for quantum characterization of the reaction dynamics to unravel the impact of the CIs in this key complex-forming reaction.…”