Structure, electronic properties and vibrational spectra of (MgF2)n clusters through a combination of genetic algorithm and DFT-based approach

Abstract

In this article, we look at the option of using a stochastic optimisation technique, namely genetic algorithm (GA) in association with density functional theory (DFT) to find out the global minimum structures of (MgF2)n clusters with the range of n being between 2 and 10. To confirm whether the structures are indeed the acceptable ones, we go on to evaluate several properties like IR spectroscopic modes, vertical excitation energy, cluster formation energy, vertical ionisation potential and the HOMO–LUMO gap. We stress on the fact that an initial estimation of structure using GA, on two empirical potentials (with and without inclusion of polarisation), leads to a very quick convergence to structures which are quite close to the structures obtained from quantum chemical calculations done from the outset, such as using a DFT calculation. The general structural trend of these systems to form three-dimensional networks is also clear from our study. The lowest energy isomers of these clusters show preference for four-membered Mg2F2 and six-membered Mg3F3 rings. In the IR spectra of (MgF2)n clusters, a blueshift of the Mg–F symmetric stretch and a redshift of asymmetric Mg–F stretching as n increases are obtained.