Isomer Lifetimes and Structure Dynamics of Sub-Nanosized Magnesium Clusters.

The properties of subnanosized metal clusters are of great interest, since they exhibit high activity in catalysis and can serve as an elemental base for nanoelectronics or quantum computing technologies. For such applications, a fundamentally important issue is the possibility of size- and structure-selective synthesis of clusters, which is largely determined by the number and energy distribution of their isomers, as well as the energy barriers to their rearrangements. Thus, the lifetimes and rates of rearrangement of isomers of subnanosized clusters is an urgent problem of both physicochemical theory and practical applications. Earlier, the complete set of magnesium cluster isomers was found in the course of global DFT optimization with subsequent optimization at the MP2/cc-pVQZ and CCSD(T)/cc-pVQZ levels. In this paper, we study the structural rearrangements of these isomers on the DFT PES by searching for transition states of their structural rearrangements and by the ADMP ab initio molecular dynamics simulation of their time evolution. The ADMP trajectory length was up to 50 ps with a step of 0.2 fs at temperatures from 300 to 700 K. The trajectories were analyzed using a specially developed algorithm for assigning trajectory points to the reference isomer structures. Based on this assignment, the average lifetimes, rearrangement probabilities, and average ratios of isomers in the equilibrium mixture were established. It is shown that the most kinetically stable structures are the Mg and Mg clusters. In contrast, other clusters at 300-400 K contain a noticeable admixture of isomeric structures.