We present a first-principles theoretical study of the atomic and electronic structures, and of the zero-temperature phases of gallium. The picture of ±-Ga that emerges is of a metallic molecular crystal with a strong Ga2 covalent bond and weaker intermolecular forces. This picture is supported in detail by the charge density, the electronic structure, and differential bond stretching under pressure. Anomalous features of ±-Ga, such as the Knight shift, anisotropic Fermi-surface effects, and optical absorption find a consistent explanation. Accurate x-ray measurements should reveal the Ga2 covalent bonds. © 1991 The American Physical Society.

Gong X. G.;Chiarotti Guido L.;Parrinello M.;Tosatti E.

Physical Review B

1991

We present results of the electronic structure and stability of some forty valence electron icosahedral Al12X (X=B, Al, Ga, C, Si, Ge, Ti, and As) clusters within the local spin density functional theory. It is shown that the stability of the Al13 cluster can be substantially enhanced by proper doping. For neutral clusters, substitution of C at the center of the icosahedron leads to the largest gain in energy. However, Al12B- is the most strongly bound in this family. These results are in agreement with the recent experiments which also find Al12B- to be highly abundant. © 1993 The American Physical Society.

Gong X. G.;Kumar Vijay

Physical Review Letters

1993

We have calculated and compared the electronic structures of both the 1D CuO-chain compound SrCuO2 and the 2D CuO2-plane material CaCuO2, on the basis of the local-spin-density approximation (LSDA) and the on-site Coulomb interaction correction (LSDA + U). The LSDA calculation gives a nonmagnetic and metallic solution as usual for CaCuO2, while it yields an antiferromagnetic (AFM) and insulating one for SrCuO2 due to the decreasing pd hybridization and the subsequent spin polarization with lowering dimensionality. Strongly in favour of orbital and spin polarizations of the Cu 3d states, the U interaction dominates in forming the charge transfer insulating character of both of the AFM cuprates. Some of the differences between the electronic structures can be qualitatively accounted for by the variance of dimensionality. © 1999 IOP Publishing Ltd.

Wu Hua;Zheng Qing-Qi;Gong Xin-Gao;Lin H. Q.

Journal of Physics Condensed Matter

1999

We have performed molecular-dynamics simulations to analyze diffusion of small clusters on a solid surface, and found a new diffusion mechanism in which a spherical-like cluster can move rapidly with a rolling motion. When applied to Ni n (n = 1-14) clusters on the Au(110)-(1×2) surface, our model predicted a cluster-size dependence in diffusion, with the most spherical-like Ni 4 and Ni 13 having the largest diffusion constants. Our model also confirmed that diffusion of Ni across the [11 ^- 0] troughs is slower than diffusion along the troughs. For the transverse diffusion, rolling of Ni 4 is, once again, an effective mode of cluster motion. © 1999 The American Physical Society.

Fan W.;Gong X. G.;Lau W. M.

Physical Review B Condensed Matter and Materials Physics

1999

The electronic structure of the large low-field magnetoresistance material CaCu3Mn4O12 is calculated by using the local-spin-density approximation (LSDA) and on-site Coulomb interaction correction (LSDA+U) to the 3d electronic states of Cu and Mn ions. The results obtained suggest a strong ionic character of this material despite a presence of a partial Mn-O covalence effect. Three Cu ions per formula cell have their respective half-filled orbitals dxy, dyz, and dxz due to their different local crystal environments. Four Mn ions per formula cell have nearly the same oxygen coordinations. As a consequence, the spin-up t2g-like orbitals (dxy,dyz, and dxz) are almost full-filled, while the spin-up eg-like orbitals (d3z2-r2 and dx2-y2) are partially occupied due to a finite pd hybridization. And it is shown that the sublattices of Cu ions and Mn ones are both aligned in ferromagnetic order, while these two sublattices are coupled antiferromagnetically, thus giving a net spin moment of 9 μB per formula. The LSDA+U calculation yields a semiconducting solution, which is improved upon a half-metallic state given by the LSDA calculation and consistent with an experimental measurement. ©2000 The American Physical Society.

Wu Hua;Zheng Q.;Gong X.

Physical Review B Condensed Matter and Materials Physics

2000

With the generalized simulated annealing algorithm (GSA), the structures and properties of Nin (n = 2-55) clusters have been studied. We find that besides the icosahedral-like structure, the structures of Ni clusters can be decahedral-like or fragments of the fee crystal. The clusters with n= 13, 38, 55 are found to be very stable. With modification of the effective coordination number model, the calculated ionization potentials of Ni clusters are in good agreement with the experimental data. The dynamical simulations show that the clusters with a closed-compact inner core have a high vibrational frequency mode, while the disordered clusters show some low vibrational frequency modes.

Xiang Y.;Sun D. Y.;Gong X. G.

Journal of Physical Chemistry A

2000

The electronic structure and the magnetism of a Mn 12 O 12 molecule at ground state have been studied by density functional theory with a local spin density approximation. We have found that the magnetic moments of Mn ions in the tetrahedron and those of Mn ions in the crown of the Mn 12 O 12 molecule align antiferromagnetically. The average moment per Mn ion is about 3.07μ B in the tetrahedron and 4.0μ B in the crown. The total spin amounts to 20.0μ B which is in agreement with recent experimental results. The significant difference of magnetic moments between Mn ions at two sites is attributed to the different exchange splitting of 3d orbitals. However, the charge difference between the two kinds of Mn ions is as small as 0.22 electrons. The charge density and the spin density exhibit strong directional dependence, which indicates the strong anisotropy in this molecule. © 1998 American Institute of Physics.

Wang S. Y.;Zou Liang-Jian;Gong X. G.;Zheng Q. Q.;Lin H. Q.

Journal of Applied Physics

1998

We have proposed a possible crystal structure for the cluster-assembled solid Al(Formula presented)C(Si), and its electronic structures and stability have been studied in the framework of density functional theory and ab initio molecular dynamics. We find that Al(Formula presented)C(Si) clusters are condensed by van der Waals force, with a very small cohesive energy of (Formula presented) 1.1 eV. The combined steepest descent on ions shows that upon the formation of solid the relaxation of atomic distances in the Al(Formula presented)C(Si) cluster is very small. The stability of the Al(Formula presented)C solid is also confirmed by a dynamical simulation at low temperature. © 1997 The American Physical Society.

Gong X.

Physical Review B Condensed Matter and Materials Physics

1997

We present results of the electronic structure and stability of calcium coverings on C60 using a linear combination of atomic orbitals and the local density functional approximation. Calculations on CaxC60 with x=12, 20 and 32 show partial charge transfer from calcium atoms to C60 and hybridization of the calcium and fullerene states. This leads to (i) a large binding energy of Ca on C60 which decreases with an increasing coverage and (ii) formation of a metallic shell on C60. The large abundance of the Ca32C60 complex is shown to be due to geometric factors in agreement with experiments. © 2001 Elsevier Science B.V.

Gong X. G.;Kumar Vijay

Chemical Physics Letters

2001

By using our newly proposed empirical interatomic potential for silicon, the structure and some dynamical properties of the silicon cluster Si n (10n clusters.

Gong X. G.;Zheng Q. Q.;He Yi-Zhen

Journal of Physics Condensed Matter

1995