A DFT Study On The Structures And Chemical Bonding Of Th_m（N₂）_n^-/0（m=1,2;n=1-6） Clusters

Thorium nitrides have important applications in the field of physics,chemistry and material science and so on due to the specific physicochemical properties of thorium nitrides,which attracts wide attention of the researchers.In order to further explore the values of potential application of thorium nitrides,it is necessary to give a micro-level research of thorium nitrides.Therefore,we are interested in exploring the internal relations among the geometric and electronic structure,chemical bonding and structural evolution of thorium nitrides at the molecular level.In this dissertation,we report the theoretical studies on the structures of thorium nitride clusters.A summary of the work is given as following:1.Theoretical calculations at the B3LYP level are employed to investigate the geometric and electronic structures,chemical bonding and structural evolution of a series of mononuclear thorium nitride clusters Th(N2)n-/0(n=1—6).Generalized Koopmans’ theorem is applied to predict the vertical detachment energies(VDEs)and simulate the photoelectron spectra(PES)of anionic ground states.According to our calculations,the ground state of Th(N2)n-(n=1-6)clusters prefers to form the low-spin structures.In terms of coordination mode,the dinitrogens are inclined to coordinate with Th atom in mode of η1 or η2.In general,the VDE trend in Th(N2)n-(n=3-6)clusters displays increases as a function of the number of dinitrogen.2.Density functional theory(DFT)calculations are performed to study a series of dinuclear thorium nitride clusters Th2(N2)n-/0(n=1-6),including identifying the structures,analyzing the chemical bonding and simulating the photoelectron spectra.The results show that Th2(N2)n(n=1-6)clusters prefer to form open-shell electronic configurations except neutral Th2N2.In the structural evolution process of neutral clusters,the Th2N2 cluster possesses four-membered ring structure.Adding dinitrogen with η2 or η1]coordination mode to the same thorium atom of Th2N2 successively yield the ground state of Th2(N2)2 and Th2(N2)3.Th2(N2)4 possesses three η1-N2 groups connecting to a same thorium atom of Th2N2.Then,the fifth and sixth dinitrogen withη1 coordination mode is added into the other thorium atom successively,which gets the ground state of Th2(N2)5 and Th2(N2)6,respectively.3.Based on the theoretical study of thorium nitride clusters,we seek the similarities and differences among the clusters derived from the reactions between small molecule(N2,NO,O2)and thorium atom in terms of structures,electron occupies and so on.Our calculated results show that all the ground state structures of clusters derived from the reactions between thorium and small molecule(NO,O2)have similarities in atomic connectivity,which involves the cleavage of O-O or N-O bond.However,the coordinated interaction occurs between thorium and dinitrogen in thorium nitride clusters.In terms of single electron occupancy,there are similarities in the ground states of anionic clusters derived from the reactions between thorium and small molecule(NO,O2).For ThO2-and ThNO-,the extra electron mainly distributes on the thorium atom;For ThO4-and ThN2O2-,single electron occupies on the coordination group.However,the extra electron is shared by thorium and two nitrogen atoms for ThN2-,and single electron occupies on the thorium atom for Th(N2)2-.