S. A. Blundell

Finite-temperature behavior of small silicon and tin clusters: An ab initio molecular dynamics study

The finite-temperature behavior of small silicon and tin clusters (Si 10 , Si 15 , Si 20 , Sn 10 , and Sn 20 ) is studied using isokinetic Born-Oppenheimer molecular dynamics. We find that the low-lying structures for all the clusters are built upon a highly stable tricapped trigonal prism unit which is seen to play a crucial role in the finite-temperature behavior. The thermodynamics of small tin clusters is revisited in light of the recent experiments on tin clusters of sizes 18-21 [G. A. Breaux et al., Phys. Rev. B, 71, 073410 (2005)]. Our calculated heat capacities for Si 10 , Sn 10 , and Si 15 show main peaks around 2300, 2200, and 1400 K, respectively. The finite-temperature behavior of Si 10 and Sn 10 is dominated by isomerization and it is rather difficult to discern their melting temperatures. On the other hand, Si 15 does show a liquidlike behavior over a short temperature range, which is followed by fragmentation observed around 1800 K. The finite-temperature behavior of Si 20 and Sn 20 shows that these clusters do not melt but fragment around 1200 and 650 K, respectively.

Charge-Induced Fragmentation of Sodium Clusters

The fission of highly charged sodium clusters with fissilities X>1 is studied by ab initio molecular dynamics. Na4+24 is found to undergo predominantly sequential Na+3 emission on a time scale of 1 ps, while Na(Q+)(24) ( 5< or =Q< or =8) undergoes multifragmentation on a time scale > or =0.1 ps, with Na+ increasingly the dominant fragment as Q increases. All singly charged fragments Na(+)(n) up to size n = 6 are observed. The observed fragment spectrum is, within statistical error, independent of the temperature T of the parent cluster for T< or =1500 K. These findings are consistent with and explain recent trends observed experimentally.

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 obtained by an all-electron linear combination of atomic orbital approach, within spin-polarized density functional theory, are reported. The binding energy, 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 polarizabilities are calculated for the ground-state structures within the GGA. It is observed that for clusters with n<9, symmetric structures with the magnesium atom occupying the internal position are higher in energy (typically by less than 1 eV) than those where Mg occupies a peripheral position. It is found that the relative ordering of the isomers is influenced by the nonlocal exchange-correlation effects for small clusters. Generalized gradient approximation extends bond lengths and ...