First Principles Study Of Structural And Electronic Properties Of Al_nN₂ (n=1-18) Clusters

It is growing more important for developing clusters of new materials in the application. Also, as the precursors for semiconductors, the study of the clusters has attracted intensive attentions. In the paper, basing on the computational method for first principles of density functional theory (full-potential linear-muffin-tin-orbital molecular dynamics method and Dmol3 program), the geometrical and electronic structures of AlnN2 clusters, which has been applied widely in the photoelectron, has been studied systematically.Firstly, we search the initial structures to find out the initial structures which are have more lower energy using the full-potential linear-muffin-tin-orbital molecular dynamics method (FP-LMTO). Then using the Dmol3 program, we optimize the selected structures and get most stable structures of AlnN2(n=1-18). Finally, we analyze the connection of the most stable structures of the clusters with the number of the Al. In the study for the ground state structures of clusters, we find that when the number of Al is equal to or below 5(n≤5), the ground states of clusters are plane. In this case, when the number of Al is 1or 2, the N-N bands have existed in the clusters. And from the number of Al n=3, the bands disappear and the appearance of Al-N bands is of importance for the steady of the clusters. However, from n=6, the stereoscopic structures of the ground structure of the clusters have appeared. For the case of form n=6 to n=11, the most stable structures of clusters are obtained by adding Al to the octahedral structure of the Al6N2. when the number of Al is larger than 12, the most stable structures of the AlnN2 clusters appear the ground state of Al13 clusters, in which the Al12N2 could be got by minusing one Al from Al13N2. And when n>13, the ground structure of cluster could be obtained by adding one Al to the icosahedral structure of Al13N2.For the properties of the ground state of the clusters, we calculate the binding energy for per atom and the second difference of energy. In the electronic structure, the HOMO-LUMO gap, the Mulliken charges, the vertical ionization potential and vertical electron affinity have been analyzed. For comparing with the results of the experiments, we calculate infrared spectrum, which supplies the theoretic fundament for the experiment in future. And through the analysis of the second difference of energy, the HOMO-LUMO gap and VIP, we find that generally when the number of Al is even, the cluster is more stable. The analysis of Mulliken charges give out that the Al-N have the properties of both of the ionicity and covalence.