An electronic structure calculation with full-potential and all-electron ab initio formalism is performed for hypothetical low-temperature simple cubic phases (Pn3 and Pa3 space groups) of C60molecular crystal, in which every molecule is orientationally freezed. The degeneracies at special k-points, the magnitudes of energy gaps, and the widths of bands have been found to be sensitive to the orientation of the fullerenes in the crystal. Our result suggests that the structure with Pa3 space group with -22° rotation around [111] directions, which David et al. proposed, is more stable compared to the structure with Pn3 space group with the same rotation angle.

Ohno Kaoru;Maruyama Yutaka;Takahashi Manabu;Yu Jing-Zhi;Gu Bing-Lin;Kawazoe Yoshiyuki

Surface Review and Letters

1996

A negatively charged donor center D- (i.e., a neutral shallow donor D0 that binds a second electron) in a spherical quantum dot is studied by use of a variational approach. A trial function which includes electron-correlation effects and approaches the Chandrasekhar-type function in the limit of zero barrier height is used. The well-radius and barrier-height dependence of the binding energy of the D- center is obtained. The dimensional characteristics are clearly demonstrated not only for the binding energy and its maximum of the D- center but also for the ratio of D- to D0 binding energy and the electron-correlation effect. © 1992 The American Physical Society.

Zhu Jia-Lin;Zhao Jie-Hua;Duan Wen-Hui;Gu Bing-Lin

Physical Review B

1992

The electronic structure of small icosahedral (Ih) silicon clusters has been studied using the discrete variational method within the local density functional theory. The Ih Si13 cluster is not a closed-shell structure, in contrast to the predictions of empirical calculations. The Si13²⁺ cluster is found to be stable, with an exceptionally large LUMO-HOMO gap.

Gu Bing-Lin;Li Zhi-Qiang;Zhu Jia-Lin

Journal of Physics Condensed Matter

1993

An eight-potential-well order-disorder ferroelectric model was presented and the phase transition was studied under the mean-field approximation. It was shown that the two-body interactions are able to account for the first-order and the second-order phase transitions. With increasing the random fields in the system, a first-order phase transition is transformed into a second-order phase transition, and furthermore, a second-order phase transition is inhibited. However, proper random fields can promote the spontaneous appearance of a first-order phase transition by increasing the overcooled temperature. The connections of the model with relaxors were discussed. © 2000 American Institute of Physics.

Liu Zhi-Rong;Gu Bing-Lin;Zhang Xiao-Wen

Applied Physics Letters

2000

The semiconducting alloy (GaSb)1-xGe2x is a member of a class of alloys that undergo order-disorder phase transitions between zinc-blende and diamond crystal structures. This transition modifies both the long-range and short-range order of the alloy as a function of composition x. This affects both thermodynamic quantities such as the order parameter, entropy, and phase diagram as well as the electronic structure, e.g., the band gap. These quantities are calculated with use of the Kikuchi approximation, combined with a correlated virtual-crystal approximation. Additionally, calculated bond probabilities are compared with extended x-ray-absorption fine structure (EXAFS) data. Both x-ray diffraction data and EXAFS data are found to be consistent with the existence in (GaSb)1-xGe2x of some wrong bonds of GaGa and SbSb. Finally, a novel violation of Vegards law for this alloy is predicted. © 1987 The American Physical Society.

Gu Bing-Lin;Newman Kathie E.;Fedders P. A.

Physical Review B

1987

The dynamics of the freezing process in relaxor ferroelectrics are investigated by Monte Carlo computer simulation. The concepts of frozen dipole and slow dipole are proposed according to the flipping frequency during the observation time of simulation. The deviation from Curie-Weiss behavior and the frequency dispersion in relaxor ferroelectrics have been proved to be caused by the increasing proportion of slow dipoles. The simulation shows that the external field reduces the dielectric constant and increases the temperature of dielectric maximum, which agrees with the experiment results. The polarization behavior with various electrical and thermal histories and starting from different initial states is also simulated and a systematic explanation based on the bifurcation tree of components in phase space is given. It is proposed that the relaxor characteristics are caused by a gradual freezing process of polar microregions, which arises from the inhomogeneous crystal structure of this kind of material. © 1995 The American Physical Society.

Gui Hong;Gu Binglin;Zhang Xiaowen

Physical Review B

1995

A method to prepare silicon nitride nanoscale rods using carbon nanotube as a template has been presented in this letter. The products of the reaction of carbon nanotubes with a mixture of Si and SiO2 powder in nitrogen atmosphere are β-Si3N4, α-Si3N4, and Si2N2O nanorods. The sizes of the nanorods are 4-40 nm in diameter and up to several microns in length. The formation mechanism of the nanorods has also been discussed. © 1997 American Institute of Physics.

Han Weiqiang;Fan Shoushan;Li Qunqing;Gu Binglin;Zhang Xiaobin;Yu Dapeng

Applied Physics Letters

1997

The low-energy theory for finite long carbon nanotube is derived and numerically examined. It shows that the electronic structure is dominated by the quantum confining, which determines the profile of wave functions as well as the eigen energies; while the details of the wave functions are resolved by the structure of the nanotubes. This behavior is attributed to the peculiar electronic structure of the nanotubes. Because of the slow variation of the profile of electron wave functions, the measured conductance is NOT independent of the position to measure it, which is evident in the multiprobe experiment. © 2000 American Institute of Physics.

Wu Jian;Duan Wenhui;Gu Bing-Lin;Yu Jing-Zhi;Kawazoe Yoshiyuki

Applied Physics Letters

2000

On the basis of the Su-Schrieffer-Heeger model and the analysis of the physical pictures of the so-called endohedral complexes Na@xaC60 and Na@xaC70, which consist of C60 and C70 molecules and a sodium ion or atom trapped inside, we have introduced two reasonable terms in the Hamiltonian to describe the interaction between the metal ion and the fullerene cage. From this simple Hamiltonian, we can reproduce the results of other first-principles calculations. Using the simplex optimization method, we have calculated the lattice distortions when all carbon atoms relax, and their effect on the potential-energy curve. Our results show that this effect is large and important. We discuss the physical meaning of our results. © 1994 The American Physical Society.

Liu Jingnan;Iwata Shuichi;Gu Binglin

Physical Review B

1994

Considering the influence of interface roughness on phonon vibrational modes in the dielectric continuum model, electron-interface phonon scattering rates are calculated in a model GaAs/Ga1-xAlxAs quantum-well structure. The intrasubband and intersubband scattering rates are given as a function of quantum-well width. It is shown that interface phonon scattering is the dominant scattering mechanism in narrow quantum-well structures and electron relaxation is strongly dependent on interface roughness. For intersubband scattering, the infinite barrier height approximation can introduce a large error, in particular, in narrow quantum-well structures. The authors' results are in good agreement with recent experimental data.

Duan Wenhui;Zhu Jia-Lin;Gu Bing-Lin

Journal of Physics Condensed Matter

1993