Ab initio investigations on planar (MgO)n clusters (n=1-5) and their hydrogen adsorption behaviour

Ab initio calculations (B3LYP and PBE-D3) of the structures, stabilities, vibrational, electronic and hydrogen adsorption behaviour of (MgO)(n) clusters are performed using 6-311+ +G(d,p) basis set. The planar (MgO)(n) clusters are found to be global minima for n3 and local minima for n=4 and 5. In addition, we have also analysed global minimum structures of (MgO)(4) and (MgO)(5). The binding energies suggest that their stabilities increase successively. Vibrational frequencies and IR intensities further support the enhanced stability with an increase in the size of (MgO)(n) clusters. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) surfaces are used to explain and discuss the electronic properties. Finally, we have demonstrated hydrogen storage capacity of (MgO)(n) clusters, considering hydrogen adsorption on planar as well as global minimum (MgO)(4) and (MgO)(5) clusters. We have noticed that four and five H-2 molecules can be easily adsorbed by (MgO)(4) and (MgO)(5) clusters having adsorption energy of 0.13-0.14eV with mass ratio of 4.76%. Thus, the present study is expected to motivate further the applications of small clusters for efficient hydrogen energy storage.