A Chebyshev method for state-to-state reactive scattering using reactant-product decoupling: OH + H2 → H2O + H

Reactant-Product Decoupling Technique Using the Intermediate Coordinate Method

Although the reactant-product decoupling (RPD) technique was proposed over two decades ago, it remains an efficient approach for calculating product state-resolved information on some simple direct reactions using the quantum wave packet method. In the past, usually the RPD technique employed the collocation method to transform the wave function between reactant and product arrangements, which requires quite large computational efforts. In this work, the intermediate coordinate (IC) method is employed to realize the RPD technique. Numerical examples demonstrate that this new IC RPD (IRPD) technique has superior computational efficiency compared with the original method employing the collocation method. Especially, the new IRPD technique significantly saves disk space and computer memory. To illustrate the features of our new method, the total reaction probabilities of the H + H2, H + Br2, and F + H2 reactions with J = 0 and the differential cross sections of the H + H2 and F + H2 reactions at a series of collision energy are calculated and presented. With this efficient and effective new RPD technique, the Li + HF reaction, which involves sharp resonances with long-range wave functions in the van der Waals wells in both the reactant and product arrangements, is also calculated with several J at the product state-resolved level to reveal the ability of the RPD technique for describing resonance wave functions. With these numerical examples, it is found that, for the reaction with resonances, the RPD approach should be applied carefully. Otherwise, it is very possible that the resonances could disappear with the application of the RPD technique.

Functional Tensor-Train Chebyshev Method for Multidimensional Quantum Dynamics Simulations

Methods for efficient simulations of multidimensional quantum dynamics are essential for theoretical studies of chemical systems where quantum effects are important, such as those involving rearrangements of protons or electronic configurations. Here, we introduce the functional tensor-train Chebyshev (FTTC) method for rigorous nuclear quantum dynamics simulations. FTTC is essentially the Chebyshev propagation scheme applied to the initial state represented in a continuous analogue tensor-train format. We demonstrate the capabilities of FTTC as applied to simulations of proton quantum dynamics in a 50-dimensional model of hydrogen-bonded DNA base pairs.

Fermi resonance controlled product branching in the H + HOD reaction

Excitation of the first overtone of bending mode results in a significant enhancement in the HD + OH channel due to the 1 : 2 Fermi resonance between the fundamental OD stretch and the first overtone of the bend.

State-to-state mode specificity in H + DOH(νOH = 1) → HD + OH(ν2 = 0) reaction: vibrational non-adiabaticity or local-mode excitation?

State-of-the-art full dimensional state-to-state quantum dynamics reveal a startling observation in which the DOH(ν_OH = 1) molecule reacts with a H atom to produce a vibrationless OH product. This interesting observation is attributed to a small OD excited local-mode component in the reactant wavefunction.

Recent advances in quantum scattering calculations on polyatomic bimolecular reactions

This review surveys quantum scattering calculations on chemical reactions of polyatomic molecules in the gas phase published in the last ten years.

Recent Advances in Quantum Dynamics of Bimolecular Reactions

In this review, we survey the latest advances in theoretical understanding of bimolecular reaction dynamics in the past decade. The remarkable recent progress in this field has been driven by more accurate and efficient ab initio electronic structure theory, effective potential-energy surface fitting techniques, and novel quantum scattering algorithms. Quantum mechanical characterization of bimolecular reactions continues to uncover interesting dynamical phenomena in atom-diatom reactions and beyond, reaching an unprecedented level of sophistication. In tandem with experimental explorations, these theoretical developments have greatly advanced our understanding of key issues in reaction dynamics, such as microscopic reaction mechanisms, mode specificity, product energy disposal, influence of reactive resonances, and nonadiabatic effects.

Modulations of Transition-State Control of State-to-State Dynamics in the F + H2O → HF + OH Reaction

The full-dimensional quantum dynamics of the F + H2O → HF + OH reaction is investigated at the state-to-state level for the first time using a transition-state wave packet method on an accurate global potential energy surface. It is found that the H2O rotation enhances the reactivity and the product-state distribution is dominated by HF vibrational excitation while the OH moiety serves effectively as a spectator. These observations underscore the transition-state control of the reaction dynamics, as both the H2O rotational and HF vibrational modes are strongly coupled to the reaction coordinate at the transition state. It is also shown that the transition-state dominance of the reaction dynamics is modulated by other features on the potential energy surface, such as the prereaction well.