Structural and spectroscopic studies of carbon dioxide clusters: a combined genetic algorithm and DFT based study

Abstract

In this manuscript we use a two-tier approach of combining stochastic search strategies and DFT calculations to arrive at extremely good quality structures for neutral (CO2) n clusters with n = 2–13. The idea of using stochastic search strategy initially is to find out extreme quickly, that is with low computational cost, more than one reasonably good structures by exploring an empirical potential energy surface for CO2 clusters. These pre-optimized structures [using genetic algorithm (GA) as stochastic optimizer] if used as inputs for subsequent DFT calculations using dispersion-corrected ωB97XD and meta hybrid M06-2X functionals give global minimum structures for these systems. This two-step strategy in our opinion is a more potent route to obtain the global minimum structures with certainty rather than a dedicated quantum chemical calculation carried from the outset. We further analyse in detail the structural, vibrational spectra and interaction energies of the clusters studied. We compare our results with experimental and theoretical results available in literature. The correspondence with experimental results is nearly 99 %, that is the results show marginal deviation from reported experimental vibrational frequencies and hence we conclude that GA in conjunction with dispersion-corrected DFT is a viable method for the study of clusters where the interaction is non-covalent in nature. Since B2PLYP-D is also an efficient functional in the study of these systems, we also report interaction energies of the cluster systems examined using this functional.