Density Functional Theory Study on the Stable Structures of Aluminum Cluster:Al5,Al5- and Al5+

Four methods (B3LYP, B3PW91，PW91PW 91，SVWN) of density functional theory with the polarized split-valence basis sets 6-311+G(3d,f) have been performed to further investigate the stable structures and the spin multiplicities for Al5，Al5-，and Al5+ clusters. For each of Al5，Al5-，and Al5+ clusters five possible structures with different spin multiplicities have been investigated respectively. Some new characteristics concerning their stable structures and spin multiplicities have been found. The stable structures obtained by four DFT methods consistently are; planar C2v-p structure with doublet state(ground state) and three-dimensional C2v-3d structure with quartet state for neutral Al5; planar C2v-p structure with single state for anionic Al5- (in the sense of vibrational averaging); three-dimensional C2v-3d structure with singlet state (ground state) and planar C2v-p structure with triplet state for cational Al5+. The adiabatic can dvertical election detachment energies ( ADE,V DE) of anionic Al5, the adiabatic and vertical ionization potentials ( AIP, VIP) of neutral Al, have been computed using the four DFT methods respectively. The comparison between presently calculated results and available experimental data as well as the previous theoretical computations has been made. The present results are in good agreement with experimental data. The comparison among calculated results obtained by the four DFT methods are also made. For general local minima or saddle points on a potential energy surface conclusions obtained by the four DFT methods arc consisted at basically, but for complicated local minima or saddle points conclusions obtained by the four DFT methods are sometimes different. It needs to further study to determine which method is relatively reliable