GAUSSIAN DENSITY-FUNCTIONAL STUDY FOR SMALL NEUTRAL (AL(N)), POSITIVE(AL(N)-) ALUMINUM CLUSTERS (N=2-5)() AND NEGATIVE (AL(N))

The structures and properties of Al(n), Al(n)+, Al(n)- (n = 1, 5) clus ters have been investigated by using the Linear Combination of Gaussia n Type Orbitals (LCGTO) method, considering Local (LSD) and Non Local (NLSD) Spin Density Approximations and employing a Model Core Potentia l (MCP) that allows the explicit treatment of 3s2 3p1 valence electron s. For each system different geometrical structures and electronic sta tes have been considered. For Al3, Al3+, Al3- the most stable geometry proved to be the equilateral triangle (D3h). Al4 and Al4+ prefer the rhombus (D2h) structure, while the corresponding anion prefers the squ are (D4h) one. The trapezoidal form (C2v) is the most stable isomer fo r Al5, Al5+ and Al5- clusters. The analysis of vibrational frequencies shows that these structures are minima in the potential energy surfac e. The binding energies (D(e)), the adiabatic ionization potentials (I P) and electron affinities (EA), the chemical potentials or absolute h ardnesses (eta) and electronegativities (CHI) have been computed. Resu lts are in good agreement with the available experimental data and the previous high level theoretical computations.