Hui-Fang Li

Density functional study of structural and electronic properties of bimetallic copper-gold clusters: comparison with pure and doped gold clusters.

The geometrical structures, relative stabilities, and electronic properties of small bare gold clusters Au(n)(lambda) and bimetallic complexes of bare metal clusters with one copper atom Au(n-1)Cu(lambda) (charge lambda = 0, +1, -1; 2 < or = n < or = 9) have been systematically investigated by means of first-principles density functional calculations at the B3LYP level. The results show that the most stable isomers have a planar structure and resemble pure gold clusters in shape, and no three-dimensional isomers were obtained for neutral and anionic doped gold clusters. However, the geometries of Au(n-1)Cu(+) are found to undergo a structural change from two dimensional to three dimensional when the cluster contains 7 atoms. The calculated dissociation energy and second difference energy as a function of the cluster size exhibit a pronounced even-odd alternation phenomenon. Ionization potentials and electron detachment energies (both vertical and adiabatic) of Au(n)(lambda) and Au(n-1)Cu(lambda) clusters are discussed and compared with available experimental results. A good agreement between experimental and theoretical results suggests good prediction of the lowest energy structures for all clusters calculated in the present study.

Structural, electronic and magnetic effects of Al-doped niobium clusters: a density functional theory study.

The application of the ab initio stochastic search procedure with Saunders “kick” method has been carried out for the elucidation of global minimum structures of a series of Al-doped clusters, NbnAl (1 ≤ n ≤ 10). We have studied the structural characters, growth behaviors, electronic and magnetic properties of NbnAl by the density functional theory calculations. Unlike the previous literature reported on Al-doped systems where ground state structures undergo a structural transition from the Al-capped frame to Al-encapsulated structure, we found that Al atom always occupies the surface of NbnAl clusters and structural transition does not take place until n = 10. Note that the fragmentation proceeds preferably by the ejection of an aluminum atom other than niobium atom. According to the natural population analysis, charges always transfer from aluminum to niobium atoms. Furthermore, the magnetic moments of the NbnAl clusters are mainly located on the 4d orbital of niobium atoms, and aluminum atom possesses very small magnetic moments.

Density functional study of the structural and electronic properties of tetra-aluminum oxide image omitted (3 n 8,=0,-1) clusters

The geometric structures, relative stabilities, and electronic properties of a series of tetra-aluminum oxide clusters, ( , ), were systematically investigated using density functional theory calculations at the B3LYP level. The optimized geometries reveal a structural transition from a two-dimensional to a three-dimensional structure for n ≤5 for the neutral species, but the three-dimensional structures are preferable for all negative clusters with the exception of . The dissociation energy, the second difference energy and the highest occupied–lowest unoccupied molecular orbital gaps as a function of the cluster size exhibit a significant even–odd alternation phenomenon. It is found that the neutral cluster is relatively stable and exhibits strong chemical stability. Furthermore, the calculated (vertical and adiabatic) electron detachment energies are also compared with previous experimental data obtained from photoelectron spectra.

Probing the structural and magnetic properties of transition metal-benzene anion complexes

Two types of transition metal-benzene anion complexes, (titanium)(n)(benzene)(m)⁻ and (cobalt)(n)(benzene)(m)⁻ (n ≤ 2, m ≤ 3) have been determined using density functional theory. The photoelectron spectra of Ti(n)Bz(m)⁻ and Co(n)Bz(m)⁻ (n ≤ 2, m ≤ 3) were discussed from the perspective of quantum chemical calculations of the vertical detachment energies (VDEs) of several low-energy isomers obtained by the structural optimization procedure. The binding of Ti and Co atoms to benzene molecules is accounted by 3d-π bonds, as revealed by the molecular orbitals. The topology of the electronic density has been analyzed, suggesting that the C-C bonds were weakened in the transition metal-benzene complexes in comparison to those in free benzene. Spin density distribution results show the spin densities for Ti(n)Bz(m)⁻ and Co(n)Bz(m)⁻ (n ≤ 2, m ≤ 3) reside mainly on the metal Ti and Co centers (70%-90%). A shift to lower magnetic moment with respect to the pure titanium/cobalt cluster anions indicates the solvent benzene molecule acts to demagnetize the bare titanium/cobalt cluster anions.

EPR and optical spectra of Ni2+-VAg in silver chloride and silver bromide

The optical absorption and EPR spectra of Ni2+-VAg centres in the AgCl:Ni2+ and AgBr:Ni2+ systems have been investigated theoretically on the basis of the complete energy matrices including the electron–electron repulsion interaction, the ligand field interaction, the spin–orbit coupling interaction, and Zeeman interaction. Because the charge compensation forms a silver ion vacancy (VAg) which makes the attractive force acted on the each ligand ion different, it was determined that the Ni–X (X = Cl, Br) distance next to VAg is shorter than others for both AgCl:Ni2+ and AgBr:Ni2+ systems in the tetragonal symmetry. Besides, it was found that the local lattice structure of (NiX6)4− clusters in AgCl and AgBr crystals exhibit a compression distortion. This compression distortion may be ascribed to the fact that the Ni2+ ion has a smaller ionic radius and more effective charge than the Ag+ ion.

Effect on the EPR and local lattice structure distortion of V(3+) ion doping corundum crystal: three models studied

This paper reports on the application of conventional models (the displacement model and the elongation model) and the four-parameter model in detecting the local molecular structure of a coordination complex. By diagonalizing the complete energy matrices, the EPR parameters and optical spectra as well as the local distortion structure for V3+ ion in the Al2O3 : V3+ system have been studied using the three models. The four-parameter model is shown to provide a significant improvement over the conventional models. Based on these calculations, it was found that when V3+ is doped in Al2O3, the distance between upper and lower ligand oxygen plane increases by 0.16097 Å and the shifts of O2− ions in the upper and lower ligand oxygen planes expand by 0.07076 Å and 0.004066 Å, respectively. To understand the detailed physical and chemical properties of the doped Al2O3, the contributions of the spin-orbit coupling to the zero-field splitting for V3+ ion are investigated.

Investigation of the Local Lattice Structure and the Effects of the Orbital Reduction Factor on the g Factors of a Trigonal [Ni(H2O)6]2+ Cluster in NiTiF6 · 6H2O and ZnSiF6 · 6H2O Crystals at Different Temperatures

The local octahedral environment of Ni2+ in NiTiF6 ・ 6H2O and ZnSiF6 ・ 6H2O crystals with a trigonal distortion has been studied at different temperatures, based on the complete energy matrices. The calculated results showed that the local lattice structure around an octahedral Ni2+ centre in NiTiF6 ・ 6H2O and ZnSiF6 ・ 6H2O exhibits a compression distortion. Simultaneously, the orbital reduction effect on the g factors has been studied. The relationship between Δg = g||−g⊥ and orbital reduction factor k at 4.2, 77 and 298 (302) K has been discussed, suggesting that there is an almost linear relation between k and Δg for the Ni2+ ion in NiTiF6 ・ 6H2O and ZnSiF6 ・ 6H2O at each temperature.