On the Bona Fide Sampling of Reaction Candidates in Red Moon Method by Replica-Exchange Molecular Dynamics Method:...

It remains challenging to microscopically simulate chemical reaction systems in which multiple chemical reactions proceed concurrently, thereby determining the overall time evolution of the system and the structure of the resulting products. For this purpose, the Red Moon (RM) method is a promising method that describes complex reaction systems by alternately using the molecular dynamics (MD) and Monte Carlo (MC) methods. However, the efficiency of the RM method strongly depends on how frequently the reactive configurations appear during the MD procedure, which can lead to inefficiencies in some systems where such configurations are rarely sampled. To overcome this limitation, we have proposed an improved version of the RM method, the REMD-RM method, which incorporates the replica-exchange molecular dynamics (REMD) method into the RM method, and applied it to two representative model systems: (i) The propylene polymerization reaction catalyzed by C₂-symmetric ansa-zirconocene complex and (ii) the radical cross-linking reaction of polypropylene. In addition to improving the efficiency of sampling reactive configurations, the REMD-RM method successfully reproduced the stereoregularity of the resulting polymer in the former case, and the temperature dependence of cross-linking reactions in the latter. Finally, we discussed the potential applicability of the REMD-RM method and the possible extension of the RM method depending on the nature of the target system.