Beyond Born–Oppenheimer constructed diabatic potential energy surfaces for F + H2 reaction

Abstract

First principles based beyond Born–Oppenheimer theory has been implemented on the F + H2 system for constructing multistate global diabatic Potential Energy Surfaces (PESs) through the incorporation of Nonadiabatic Coupling Terms (NACTs) explicitly. The spin–orbit (SO) coupling effect on the collision process of the F + H2 reaction has been included as a perturbation to the non-relativistic electronic Hamiltonian. Adiabatic PESs and NACTs for the lowest three electronic states (12A′, 22A′, and 12A″) are determined in hyperspherical coordinates as functions of hyperangles for a grid of fixed values of the hyperradius. Jahn–Teller (JT) type conical intersections between the two A′ states translate along C2v and linear geometries in F + H2. In addition, A′ and A″ states undergo Renner–Teller (RT) interaction at collinear configurations of this system. Both JT and RT couplings are validated by integrating NACTs along properly chosen contours. Subsequently, we have solved adiabatic-to-diabatic transformation (ADT) equations to evaluate the ADT angles for constructing the diabatic potential matrix of F + H2, including the SO coupling terms. The newly calculated diabatic PESs are found to be smooth, single-valued, continuous, and symmetric and can be invoked for performing accurate scattering calculations on the F + H2 system.

Accurate Calculation of Rate Constant and Isotope Effect for the F + H2 Reaction by the Coupled 3D Time-Dependent Wave Packet Method on the Newly Constructed Ab Initio Ground Potential Energy Surface

“…On the other hand, Li et al constructed a new PES employing double many-body expansion (DMBE) on the basis of MRCI+Q ab initio calculation. Later, in a series of studies, the role of Jahn–Teller and Renner–Teller conical intersections for this title system was investigated by Das et al − Most recently, Adhikari and co-workers calculated the lowest three adiabatic PESs of F + H 2 (1 2 A′, 2 2 A′, and 1 2 A″) and the nonadiabatic coupling terms (NACTs) between those states, where first-principles based beyond Born–Oppenheimer (BBO) theory , was employed for an accurate description of nuclear coupling while generating multistate diabatic PESs the effect of SO coupling. At this point, it is noteworthy that a generalized algorithm, “ADT” has recently been developed by Adhikari and co-workers to construct theoretically “exact” and numerically “accurate” diabatic PESs for any number of coupled nuclear degrees of freedom (DOF) and electronic states.…”

“…At this point, it is noteworthy that a generalized algorithm, “ADT” has recently been developed by Adhikari and co-workers to construct theoretically “exact” and numerically “accurate” diabatic PESs for any number of coupled nuclear degrees of freedom (DOF) and electronic states. A more detailed literature survey on the various FH 2 PESs with different levels of accuracy could be found elsewhere and in the references therein.…”

Neural Network Representation of Three-State Quasidiabatic Hamiltonians Based on the Transformation Properties from a Valence Bond Model: Three Singlet States of H3+

“…Since the information of the derivative couplings is crucial to analyze the local topography of conical intersection and avoided-crossing regions, the derivative-based methods should be most rigorous for real applications to construct accurate quasidiabatic representations. Many efforts have been made to develop derivative-based methods, including (1) solving the Poisson equation, − (2) the Shepard interpolation-based method, − (3) the beyond Born–Oppenheimer (BBO) treatment, − and (4) simultaneously fitting and diabatizing with symmetry-adapted polynomials − by Zhu and Yarkony (ZY). Particularly, the resulting diabatic representations by Zhu and Yarkony (ZY) with symmetry-adapted polynomials are generated in a least-squares sense, which are reliable due to the explicit minimization of fitting errors of derivative couplings. , Some recent studies have been mainly focused on fitting and diabatizing, using neural networks (NNs) to achieve higher accuracy. ,− …”

Investigation of nonadiabatic coupling and diabatic electronic population dynamics on F2O+ cation within multi reference configuration interaction calculations

“…For about a century, the theory known as Born–Oppenheimer approximation (BOA) [18] has been used to solve the molecular Schrödinger equation. The success of the BOA depends primarily on the difference between the masses of the electrons and the nucleus, which makes it possible to separate the electron motion from the nuclear motion [19, 20]. In fact, electronic motion is parametrically dependent on the motion of nuclei.…”

“…In BOA, we can describe some of the chemical processes that mainly occur at lower energy regions of ground electronic state. In nature, a wide range of molecular phenomena (that involve electronically excited states such as photosynthesis, vision, charge transfer chemical reactions and solar energy conversion to photochemical reactions) occur beyond the BO approximation (BBO), when the coupling of electronic and nuclear motions leads to non‐adiabatic events [19, 20]. The forces governing the motion of the nucleus in a molecule are determined by adiabatic potential energy surfaces (PESs) and non‐adiabatic coupling terms (NACTs), which are the result of the BOA.…”