Gao-feng Zhao

Computational investigation of TiSin (n=2-15) clusters by the density-functional theory.

The geometries, stabilities, and electronic properties of TiSin (n=2-15) clusters with different spin configurations have been systematically investigated by using density-functional theory approach at B3LYP/LanL2DZ level. According to the optimum TiSin clusters, the equilibrium site of Ti atom gradually moves from convex to surface, and to a concave site as the number of Si atom increases from 2 to 15. When n=12, the Ti atom in TiSi12 completely falls into the center of the Si outer frame, forming metal-encapsulated Si cages, which can be explained by using 16-electron rule. On the basis of the optimized geometries, various energetic properties are calculated for the most stable isomers of TiSin clusters, including the average binding energy, the highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO) gap, fragmentation energy, and the second-order difference of energy. It is found that at size n=6,8,12 the clusters are more stable than neighboring ones. According to the Mulliken charge population analysis, charges always transfer from Si atoms to Ti atom. Furthermore, the HOMO-LUMO gaps of the most stable TiSin clusters are usually smaller than those of Sin clusters.

Density-functional study of structural, electronic, and magnetic properties of the EuSin (n=1–13) clusters

The geometries, stabilities, and electronic and magnetic properties of europium encapsulated EuSi(n) (n=1-13) clusters have been investigated systematically by using relativistic density functional theory with generalized gradient approximation. Starting from n=12, the Eu atom completely falls into the center of the Si frame, i.e., EuSi(12) is the smallest fully endohedral Eu silicon cluster. The interesting finding is in good agreement with the recent experimental results on the photoelectron spectroscopy of the europium silicon clusters [A. Grubisic, H. P. Wang, Y. J. Ko, and K. H. Bowen, J. Chem. Phys. 129, 054302 (2008)]. The magnetic moments of the EuSi(n) (n=1-13) clusters are also studied, and the results show that the total magnetic moments of the EuSi(n) clusters and the magnetic moments on Eu do not quench when the Eu is encapsulated in the Si outer frame cage. It is concluded that most of the 4f electrons of the Eu atom in the EuSi(12) cluster do not interact with the silicon cage and the total magnetic moments are overwhelming majority contributed by the 4f electrons of the Eu atom. According to the binding energy per atom, the second difference in energy (Delta(2)E), and vertical ionization potential, the EuSi(n) (n=4,9,12) clusters are very stable.

A density functional study of YnAl (n=1–14) clusters

The geometries, stabilities, and electronic and magnetic properties of Y(n)Al (n=1-14) clusters have been systematically investigated by using density functional theory with generalized gradient approximation. The growth pattern for different sized Y(n)Al (n=1-14) clusters is Al-substituted Y(n+1) clusters and it keeps the similar frameworks of the most stable Y(n+1) clusters except for Y(9)Al cluster. The Al atom substituted the surface atom of the Y(n+1) clusters for n<9. Starting from n=9, the Al atom completely falls into the center of the Y-frame. The Al atom substituted the center atom of the Y(n+1) clusters to form the Al-encapsulated Y(n) geometries for n>9. The calculated results manifest that doping of the Al atom contributes to strengthen the stabilities of the yttrium framework. In addition, the relative stability of Y(12)Al is the strongest among all different sized Y(n)Al clusters, which might stem from its highly symmetric geometry. Mulliken population analysis shows that the charges always transfer from Y atoms to Al atom in all different sized clusters. Doping of the Al atom decreases the average magnetic moments of most Y(n) clusters. Especially, the magnetic moment is completely quenched after doping Al in the Y(13), which is ascribed to the disappearance of the ininerant 4d electron spin exchange effect. Finally, the frontier orbitals properties of Y(n)Al are also discussed.

The structural and electronic properties of InnN(n=1–13) clusters

The structural and electronic properties of In(n)N(n=1-13) clusters have been investigated by density-functional theory with the generalized gradient approximation. The results indicate that the equilibrium structures of In(n)N are linear for n=1,2, planar for n=3-5, and three dimensional for n=6-13. Maximum peaks were observed for In(n)N clusters at n=3,7,9 on the size dependence for second-order energy difference. These imply that these clusters possess relatively higher stability, which is consistent with the case of binding energy per atom. Moreover, the results show that the bonding in small In(n)N clusters has a little ionic character by Mulliken population analysis. The energy gap between the highest occupied and lowest unoccupied molecular orbitals, the vertical ionization potential and electron vertical affinity (VIP and VEA) form an even-odd alternating pattern with increasing cluster size. In general, the VIP tends to lower as the cluster size increases, while the VEA tends to increase as the cluster size increases.

The structural and electronic properties of Ag-adsorbed (SiO2…n )(n=1–7) clusters

Equilibrium geometries, charge distributions, stabilities, and electronic properties of the Ag-adsorbed (SiO(2))(n) (n=1-7) clusters have been investigated using density functional theory with generalized gradient approximation for exchange-correlation functional. The results show that the Ag atom preferably binds to silicon atom with dangling bond in nearly a fixed direction, and the incoming Ag atoms tend to cluster on the existing Ag cluster leading to the formation of Ag islands. The adsorbed Ag atom only causes charge redistributions of the atoms near itself. The effect of the adsorbed Ag atom on the bonding natures and structural features of the silica clusters is minor, attributing to the tendency of stability order of Ag(SiO(2))(n) (n=1-7) clusters in consistent with silica clusters. In addition, the energy gaps between the highest occupied and lowest unoccupied molecular orbitals remarkably decrease compared with the pure (SiO(2))(n) (n=1-7) clusters, eventually approaching the near infrared radiation region. This suggests that these small clusters may be an alternative material which has a similar functionality in treating cancer to the large gold-coated silica nanoshells and the small Au(3)(SiO(2))(3) cluster.

Structural, electronic, and magnetic properties of MB{sub n} (M=Cr,Mn,Fe,Co,Ni, n{<=}7) clusters

We have investigated the stability, electronic, and magnetic properties of transition-metal-doped MB{sub n} clusters (M=Cr,Mn,Fe,Co,Ni, n{<=}7) using first-principles density functional theory with generalized gradient approximation. The equilibrium structures of MB{sub n} (n{<=}5) clusters can be obtained by directly adding M atoms to the B{sub n} clusters, while for n=6, hexagon or near-hexagon geometries with a boron atom at the center ring are regarded as the ground-state structures. n=7 marks the onset of three-dimensional geometries for MB{sub n} clusters. According to the second-order energy differences, gaps between the highest occupied molecular orbital and lowest unoccupied molecular orbital and vertical ionization potentials, we can conclude that CrB{sub 4}, CrB{sub 7}, MnB{sub 3}, FeB{sub 3}, FeB{sub 5}, FeB{sub 7}, and CoB{sub 7} possess relatively higher stabilities. The relative orientation between the magnetic moments of the M atom and those of its neighboring B atoms mainly exhibits an antiferromagnetic alignment for CrB{sub n}, MnB{sub n}, and FeB{sub n}, while it mainly shows a ferromagnetic alignment for CoB{sub n} and NiB{sub n} clusters.