Adiabatic Trajectory Approximation within the Framework of Mixed Quantum/Classical Theory

Authors

Bikramaditya Mandal, Marquette University
Alexander Semenov, Marquette UniversityFollow
Dmitri Babikov, Marquette UniversityFollow

Document Type

Article

Publication Date

2020

Publisher

American Chemical Society

Source Publication

Journal of Physical Chemistry A

Source ISSN

1089-5639

Abstract

A hierarchy of approximate methods is proposed for solving the equations of motion within a framework of the mixed quantum/classical theory (MQCT) of inelastic molecular collisions. Of particular interest is a limiting case: the method in which the classical-like equations of motion for the translational degrees of freedom (scattering) are decoupled from the quantum-like equations for time evolution of the internal molecular states (rotational and vibrational). In practice, trajectories are pre-computed during the first step of calculations with driving forces determined solely by the potential energy surface of the entrance channel, which is an adiabatic trajectory approximation. Quantum state-to-state transition probabilities are computed in the second step of calculations with an expanded basis and very efficient step-size adjustment. Application of this method to H₂O + H₂ rotationally inelastic scattering shows a significant computational speedup by 2 orders of magnitude. The results of this approximate propagation scheme are still rather accurate, as demonstrated by benchmarking against more rigorous calculations in which the quantum and classical equations of motion are held coupled and against the full-quantum coupled-channel calculations from the literature. It is concluded that the AT-MQCT method (the adiabatic trajectory version of MQCT) represents a promising tool for the computational treatment of molecular collisions and energy exchange.

Comments

Accepted version. Journal of Physical Chemistry A, Vol. 124, No. 47 (2020): 9877-9888. DOI. © 2020 American Chemical Society. Used with permission.

Recommended Citation

Mandal, Bikramaditya; Semenov, Alexander; and Babikov, Dmitri, "Adiabatic Trajectory Approximation within the Framework of Mixed Quantum/Classical Theory" (2020). Chemistry Faculty Research and Publications. 1016.
https://epublications.marquette.edu/chem_fac/1016