About
9000 structures of magnesium clusters Mg
n
(n = 2–13) generated via different
methods were optimized at the DFT levels in order to estimate the
number of all possible stable structures that can exist for the given
cluster size (∼820,000 PES points were explored in total).
It was found that the number of possible cluster isomers N quickly grows with a number of atoms n; however,
it is significantly lower than the number of possible nonisomorphic
graph structures, which can be drawn for the given n. At the DFT potential energy surface, we found only 543 local minima
corresponding to the isomers of Mg2–Mg13. The number of isomers obtained in the DFT optimizations grows with n approximately as n
4, whereas
the N values extrapolated to the infinite generation
process grow as n
8. The cluster geometries
obtained from the global DFT optimization were then used to adjust
two empirical potentials of Gupta type (GP) and modified Sutton-Chen
type (SCG3) describing the interactions between the magnesium atoms.
Using these potentials, the extensive sets of structures Mg2-Mg55 (up to 30,000 clusters for each n) were optimized to obtain the dependence of the cluster isomer count
on n in the continuous range of n = 2–30 and for selected n up to n = 55. It was found that the SCG3 potential, which is closer
to the DFT results, gives a number of possible isomers growing as
approximately n
8.9, whereas GP potential
results in the n
4.3 dependence.