Density Functional Theory Study Of (PdH)_N(N=10-35) And(LiBH₄)_N(N=3-12) Nanoclusters

In this paper,the global energy minimum configurations of(PdH)N(N=10-35)and(LiBH4)N(N=3-12)nanoclusters were obtained based on the colony algorithm combined with density functional theory.The structural properties,electronic properties and bonding behavior of the clusters were investigated.The results show that the global stable structure of(PdH)N shows spherical disorder,and the H atoms are generally distributed on the surface in the formation of two-fold bridge or three-fold hollow sites.Specially,there are some H atoms in the form of relaxed molecular side bonds to the Pd atom,which are called Kubas bond.Stability analysis shows that the formation process of clusters is thermodynamically favorable,and the stability of clusters increases with increasing cluster size.The bond length analysis of the structure shows that the bond length of Pd-Pd stretch since the H weakens the interaction between Pd atoms.The coordination number of Pd showed an upward trend with the increase of the cluster size,but the coordination number of Pd-H fluctuated between 2-3 due to the similarity of hydrogen occupation mode in different clusters.With respect to the calculation of electronic properties,it shows that electrons generally transfer from Pd to H,and the amount of atomic charge is related to the distribution location and bonding type of atoms.The density of states identified the major bonding area of Pd-Pd and Pd-H,as well as the semi-metallic properties of the clusters with no magnetism or weakly magnetism.In addition,the crystal orbital Hamiltonian population analysis of(PdH)35 nanocluster was performed to identify the interaction differences between Pd and various H atoms.The results show that there is a linear relationship between the bond strength and bond length of Pd-H bond.Under similar bond length condition,the interaction of Pd-H bond is strongest for the isolated surface H atoms and the weakest for the Kubas type.Occupied molecular orbitals provides a consistent graphic interpretation of the bonding peaks.Finally,the effects of H load for binding energy of H and d band center are discussed.For the ground state structure of(LiBH4)N nanoclusters,at N=3-5,clusters are more inclined to form a closed-loop plane-like structure with spacing distribution of Li atom and[BH4]group,while larger clusters show a relatively disordered three-dimensional configuration with local closed-loop.The transformation of clusters from closed-loop structure to three-dimensional configuration leads to the average bond lengths of Li-H and Li-B significantly increased,but the average bond lengths of B-H are similar among all clusters in our system.Average binding energy analysis shows a general trend that the stability of nanoclusters increases with the increase of the number of primary units.The electron localization function calculation indicates that the Li atom and the[BH4]group combine in the form of ionic bond,and the inside of[BH4]group is the form of covalent bond.The sum of bond order of atoms and the bond order of chemical bonds exploration further confirmed the conclusion of bond properties.The charge analysis demonstrates that electrons transfer from the Li atom to the[BH4]group.The negative charge in the group is mainly concentrated on B atom,while H atoms is slightly electronegative.The analysis of density of states exhibits that the bonding region is mainly due to the interaction between B and H atoms,while the overall contribution of Li atoms is weak and more involved in the antibonding region.The clusters are insulated according to the results of gap calculation.