摘要
用一维复式晶格作为反式聚乙炔的模型 ,在周期与非周期边界条件下 ,考虑链端效应并计及电子的非近邻跳跃 ,数值计算了格点数分别等于N =10、5 0、10 0和 2 0 0时聚乙炔的能谱和态密度 .讨论了不同格点数和结构参数对态密度及带宽的影响 ,并对两种边界条件下的计算结果进行了比较 .计算结果表明 ,当格点数N <5 0时 ,两者相差较大 ,这表明系统的边界将起很大作用 ;当格点数N≥ 5 0时 ,两者相差甚微 ,这时可利用周期性边界条件来研究有限系统问题 .
As the real trans-polyacetylene molecule has finite chain length, its chain-terminal effects on various properties should be taken into account, that is to say, the aperiodic boundary condition should be employed in studying the properties of conducting polymers. However, if trans-polyacetylene chain is long enough, the chain-terminal effects can be ignored. In this paper, a one-dimensional finite compound lattice model of trans-polyacetylene chain is adopted. With considering the chain-terminal effects and the next-neighbor hopping interactions, the energy spectra and the density of states are calculated for trans-polyacetylene chains with the lattice number N from 10 to 200 under the periodic and aperiodic boundary conditions. The effects of chain length and interaction parameter on density of states and band width are also discussed. It is shown that the curves of DOS, are symmetrical when the nearest-neighbor hopping is merely considered, and the valence and conduction bands are unsymmetrical when the next-neighbor term is taken into account. At the same time, some results under two kinds of boundary conditions are compared. When N < 50, the surface states appear under the aperiodic boundary condition, as well as DOS nearby the Feimi surface is larger than that under the periodic boundary condition. When N greater than or equal to 50, the surface states are difficult to distinguish between the valence and conduction bands, and DOS tends to be identical under two kinds of boundary conditions. Moreover, with N increasing, the difference of ionization energy under the two boundary conditions is reduced for the same parameter. In conclusion, when N < 50, there is a large difference for nearest-neighbor hopping and next-neighbor hopping due to the chain-terminal affect. This indicates that the aperiodic boundary condition plays an important role in dealing with finite systems. However, when N greater than or equal to 50, since the chain-terminal effect can be neglected, the periodic boundary condition is suitable for the finite trans-polyacetylene system.
出处
《高分子学报》
SCIE
CAS
CSCD
北大核心
2003年第3期374-380,共7页
Acta Polymerica Sinica
基金
国家自然科学基金 (基金号 2 98740 2 1
2 0 1740 2 1和 2 0 2 740 40 )
浙江省自然科学基金 (基金号 10 10 0 2 )资助项目
