Abstract

This chapter is exclusively devoted to molecular clusters. Molecular clusters refer to finite aggregates of molecules or compounds. In such clusters, molecules are usually bound by hydrogen bonding, van der Waals, or similar weak interactions. We have shown some examples of molecular clusters, such as the clusters of H2O and LiF molecules. Alkaline-earth metal oxide clusters such as (BeO)N , (MgO)N , and (CaO)N have specifically been discussed, and their hydrogen storage behavior have been explored using various DFT methods such as B3LYP, PBE-D3, M06-2X, etc. B3LYP is a hybrid functional. PBE-D3 is a dispersion-corrected GGA functional, whereas M06-2X is a meta GGA functional, as discussed in Chapter 1. It was found that small (BeO)N clusters prefer planar structures due to partially covalent Be-O bonds, unlike ionic Mg-O and Ca-O bonds. Although all these clusters can effectively adsorb H2 molecules, smaller clusters serve as better adsorbents due to the high percentage mass ratio.