Theoretical Studies On The Structure,Electronic Properties And Chemical Bonding Of (VH₂)_n(n=10-30) Nanoclusters And (NiH₂)_n(n=10-35) Nanoclusters

The hydrogen storage performance of transition metal hydrides has been broadly investigated in experimen and theory.The view of using nanoparticles to develop the hydrogen storage work of metal hydrides has obtained broadly consideration.However,the nanoscale VH2 and NiH2 clusters have not been fully studied,so it was decided to systematically investigate(VH2)n(n=10-30)and(NiH2)n(n=10-35)clusters by means of theoretical calculations.In the(VH2)n(n=10-30)system,hydrogen atoms are mostly attached to three vanadium atoms,which have irregular structures.The calculated average distance between V and V and the average distance among V and H are very close to the value in the bulk.The coordination numbers in(VH2)n(n=10-30)clusters are vary from those in VH2 crystals.In this system,when n values are 12,16,18,and 26,relatively speaking,these clusters are more stable than their neighboring structures,because the average binding energy values of these structures are bigger than those of their adjoining structures.In addition,?bonds are found in the cooperation between the V-d and H-s orbitals.The total bond order value of these clusters in the 3c-2e system is less than that in the 4c-2e combinations.These clusters are more likely to design 4c-2e combinations than 3c-2e combinations.In the V24H48 and V29H58,it was found that the charge values on some hydrogen atoms were positive,and the Kubas interaction was further investigated.However,the consequence of this effect is to make the distance between H2 and V further.In the(NiH2)n(n=10-35)nanoclusters,most of the H atoms are distributed on the surface of the clusters and tend to build two coordinated and three coordinated structures.Most of the Ni atoms diffuse in the inner part of the cluster,which constitutes the basic framework of the whole structure.H atoms are distributed on the surface of the structure and are connected with Ni atoms.By calculating the average binding energy,it is found that Ni13H26,Ni19H38,Ni21H42,Ni24H48,Ni26H52,Ni28H56,Ni31H62 and Ni35H70 clusters have higher average binding energy than their adjoining clusters.The Ni-d and H-s orbitals have large interactive parts in the energy range of-6 eV--3 eV.Due to the Kubas interaction,the ? orbital of H2 afford the electron density for the d orbital of Ni atom.The stronger bond states of the Ni-H pairs with this interaction occur at an energy of about-8.5 eV,which is lower than that of the normal Ni-H pairs without this action,indicating that the Ni-H pairs with this action need a lower energy to have a certain bond state.The ? and ? bonds are built by the intersections of the d orbitals of Ni atoms.The ? bond is found to exist in the superposition of the s orbitals of H and the d orbitals of Ni atoms.The hybridization of the orbitals among Ni and H atoms yield a strong Ni-H bond,which causes the structures stronger.