Density functional study of structural and electronic properties of NanMg (1 <= n <= 12) clusters

Low-lying equilibrium geometric structures of NanMg (n=1-12) clusters obtai ned by an all-electron linear combination of atomic orbital approach, withi n spin-polarized density functional theory, are reported. The binding energ y, dissociation energy, and stability of these clusters are studied within the local spin density approximation (LSDA) and the three-parameter hybrid generalized gradient approximation (GGA) due to Becke-Lee-Yang-Parr (B3LYP) . Ionization potentials, electron affinities, hardness, and static dipole p olarizabilities are calculated for the ground-state structures within the G GA. It is observed that for clusters with n <9, symmetric structures with t he magnesium atom occupying the internal position are higher in energy (typ ically by less than 1 eV) than those where Mg occupies a peripheral positio n. It is found that the relative ordering of the isomers is influenced by t he nonlocal exchange-correlation effects for small clusters. Generalized gr adient approximation extends bond lengths and widens the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied mo lecular orbital (LUMO), as compared to the LSDA gap. The odd-even oscillati ons in the dissociation energy, the second differences in energy, the HOMO- LUMO gaps, the ionization potential, the electron affinity, and the hardnes s are more pronounced within the GGA. The stability analysis based on the e nergetics clearly shows the Na6Mg cluster to be endowed with special stabil ity, which occurs because of an electronic shell closure. (C) 2001 American Institute of Physics.