Density Functional Theory Study Of Structural And Electronic Properties Of (HfH₂)_n(n=5-30)and(LiH)_n(n=5-25)Nanoclusters

Our thesis work aspires to analyze the behavior of Hafnium hydride and Lithium hydride nanoclusters for the purpose to potentially store hydrogen.Currently available fossil fuels are primary source of energy required to move the human beings'necessities but these fuels are constantly diminishing due to excessive use.Moreover,due to adequately use of fossil fuels,climate change is also becoming a serious concern.To mitigate such issues,an alternate energy source is quite essential to fulfill the energy demand and must also be environmentally friendly to minimize the adverse effect to global warming.Among them,hydrogen is considered to be an ideal energy carrier required for future transport.A major obstacle to replace fossil-based economy to hydrogen economy requires to solve some challenges including the storage of hydrogen.The available conventional gaseous state storage system and cryogenic liquid storage system are unsafe,heavy and very cost expensive and do not satisfy the future demands for hydrogen economy.For the improvement of hydrogenation properties,intensive research had been done.In our thesis,we have studied the kinetics of hafnium and lithium chemically bounded to hydrogen to store hydrogen.For the HfH2 clusters,different sizes ranging from 5-30 were studied to perceive their behavior.And also,for the LiH nanoclusters,the properties of different size ranged clusters were also studied to observe the behavior of these clusters.For solid-state hydrogen storage,(HfH2)clusters were considered to be a promising candidate because of being possessing higher hydrogen capacity,lower cost and greater affinity between the interacting atoms.The structural and electronic properties of(HfH2)n clusters are investigated by employing the density functional theory.From the DFT calculations,it is found that Hf atom occupies central position while H atoms tends to occupy at vertex spots.Through stability analysis,the calculated binding energy and second order energy difference of(HfH2)n clusters increases from(HfH2)5 through(HfH2)30 cluster.The charge density distribution and results of Bader analysis also revealed ionic bonding character between Hf and H atoms and transfer of electrons is observed from Hf to H atoms.The orbital overlapping contribution of the interacting Hf and H atom is also performed to understand the bonding strength.Moreover,first principles calculations have also been performed to analyze the structural and electronic properties of(LiH)n clusters by combining artificial bee colony algorithm within the framework of density functional theory(DFT).The structural analysis shows that with increase in cluster size structural shape tends to become more amorphous in which lithium atom occupies the central position surrounded by hydrogen atom at vertex sites.The bond length between Li and H was found to be 1.77-2.01 A which is in good agreement with the previous study.Through stability analysis,the calculated formation energy and cohesive energy of LiH clusters increases from n=5 through n=25.The projected density of states(PDOS)was calculated and analyzed to get deep insights into the electronic structure.The charge density distribution and results of DDEC6 analysis revealed ionic bonding character between Li and H atoms and charge density difference analysis concludes electron transfers from Li to H atoms.