Jianhua Wei

Effects of boundary conditions on the stability of one-dimensional Peierls-Hubbard systems

Several boundary conditions have been proposed to stabilize the dimerized structures of finite-length Peierls-Hubbard chains. The effects of different boundary conditions on the lattice structures and the electronic energy spectra have been analysed. It was found that the natural or the fixed-end boundary conditions are more suitable to describe polymer chains with very short lengths than the periodic boundary condition. The competition of electron-electron interactions with electron-phonon interactions in finite-length chains has also been studied.

Effect of atomic disorder or chain length on the stability of photoinduced polarization inversion

The effect of atomic disorder or chain length on the stability of photoinduced polarization inversion has been studied. The atomic disorder was simulated by square-random or Gaussian-random model. It was found that for the square-random distribution case, photoinduced polarization inversion remains steadily when atomic disorder is less than 18a (a is the lattice constant of polyacetylene), the reversion polarization disappears and gets into normal polarized state when the disorder is stronger than over 18a. The reason of a normal polarization resulted from the strong lattice disorder was discussed. The relationship between the reverse polarization of biexciton state and the confinement constant te as well as the variation of chain length was also studied.

Dimensional model of carbon nanotubes

A dimensional model was set up to study the electronic and lattice property of single-walled carbon nanotubes. The calculations clearly confirmed the experimental results, which included that armchair-type nanotubes were metallic, zigzag-type semiconductive or metallic depending upon the charity and tube diameters. Our investigation revealed that the quasi-one dimension was the essential characteristic of carbon nanotubes.

NHY coupling model in PtX compounds

Abstract An Nue5f8Hue5f8Y coupling model was supposed on a two-chain system of Ptx (X = Cl, Br, I) to study the role of interchain coupling. It was found that the CDW and BOW are suppressed by the interchain coupling and the CT gap decreases, which is consistent with the pressure experiments of MX compounds.

Quantum Charge Transfer in Quasi-One-Dimensional Mixed Halide Compounds

Intrinsic charge transfer in mixed halide compounds PtXxX1-x was studied in the framework of the two-band extended Pielerls-Hubbard model. It was found that the number of transferred charges can be a fraction times of the electronic charge. The maximum amount of the transferred charges will occur at a certain proportion x for a given mixed compound.

Electric-Field Control on Polaron Tunnelling in Copolymers

We present a calculation of the electric-field control on polaron tunneling in triblock copolymers that have a double-well structure. It was found that there exists a critical electric-field values, E c1 (or E c2 =-E c1 in the opposite direction). At the critical value, a polaron can tunnel the barrier and enter the other well. The properties of polaron tunnelling should be favourable to fabricating the devices of molecular memories or switches.

Shallow energy levels around solitons, polarons and bipolarons in quasi-one-dimensional MX compounds

Shallow energy levels in quasi-one-dimensional MX compounds have been found firstly by considering the two-band tight-binding model. These shallow levels are situated at the band edges of the CB and VB. The electronic states of the shallow levels are localized around solitons, polarons and bipolarons. It is expected that these shallow levels could be observed in the absorption spectrum of MX compounds. Finally, the effect of e-e interactions on the shallow levels was studied. It has been found that e-e interactions will decrease the mini-gap between the shallow levels and CB and increase the mini-gap between the shallow levels and VB.