Metadynamics molecular dynamics and isothermal Brownian-type molecular dynamics simulations for the chiral cluster...

In an effort to gain insight into enantiomeric transitions, their transition mechanism, time span of transitions and distribution of time spans etc, we performed molecular dynamics (MD) simulations on chiral clusters Au₁₀, Au₁₅and Au₁₈, and found that viable reaction coordinates can be deduced from simulation data for enlightening the enantiomeric dynamics for Au₁₀and Au₁₅, but not so for Au₁₈. The failure in translating the Au₁₈-L ⇌ Au₁₈-R transitions by MD simulations has been chalked up to the thermal energyk_BTat 300 K being much lower than energy barriers separating the enantiomers of Au₁₈. Two simulation strategies were taken to resolve this simulation impediment. The first one uses the well-tempered metadynamics MD (MMD) simulation, and the second one adeptly applies first a somewhat crude MMD simulation to locate a highly symmetrical isomer Au_18Sand subsequently employed it as initial configuration in the MD simulation. In both strategies, we work in collective variable space of lower dimensionality. The well-tempered MMD simulation tactic was carried out aiming to offer a direct verification of Au₁₈enantiomers, while the tactic to conduct MMD/MD simulations in two consecutive simulation steps was intended to provide an indirect evidence of the existence of enantiomers of Au₁₈given that energy barriers separating them are much higher than ca.k_BTat 300 K. This second tactic, in addition to confirming indirectly Au₁₈-L and Au₁₈-R starting from the symmetrical cluster Au_18S, the simulation results shed light also on the mechanism akin to associative/nonassociative reaction transitions.