The method of Gaussian weighted trajectories. V. On the 1GB procedure for polyatomic processes

TL;DR

This paper discusses the 1GB procedure, a computationally efficient method for simulating polyatomic chemical reactions, supported by theoretical arguments and validated through model tests and a four-atom reaction case.

Contribution

It provides theoretical justification for the 1GB method and demonstrates its effectiveness on test cases and a specific four-atom reaction.

Findings

1GB reduces computational cost by a factor of about 10 compared to traditional GB.

Theoretical arguments support the validity of the 1GB procedure.

Validation on model and real reactions confirms the method's accuracy.

Abstract

In recent years, many chemical reactions have been studied by means of the quasi-classical trajectory (QCT) method within the Gaussian binning (GB) procedure. The latter consists in "quantizing" the final vibrational actions in Bohr spirit by putting strong emphasis on the trajectories reaching the products with vibrational actions close to integer values. A major drawback of this procedure is that if N is the number of product vibrational modes, the amount of trajectories necessary to converge the calculations is ~ 10^N larger than with the standard QCT method. Applying it to polyatomic processes is thus problematic. In a recent paper, however, Czako and Bowman propose to quantize the total vibrational energy instead of the vibrational actions [G. Czako and J. M. Bowman, J. Chem. Phys., 131, 244302 (2009)], a procedure called 1GB here. The calculations are then only ~ 10 times more time-consuming than with the standard QCT method, allowing thereby for considerable numerical saving. In this paper, we propose some theoretical arguments supporting the 1GB procedure and check its validity on model test cases as well as the prototype four-atom reaction OH+D_2 -> HOD+D.