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本文运用羣论方法,把不稳定局域模和含杂晶格的带内本征矢的散射部分都按格位羣的不可约表示分了类。具体地讨论了最近邻相互作用的简单立方晶格的情况,计算结果表明:可。能产生同P(=γ′/γ)和(=m′/m)有关的T1u型不稳定局域模和仅与P有关的简并的A1g,Eg,T1g,T2g和简并的T1u,T2u型不稳定局域模,以及只有同一类型的对称性驻波才能为杂质所散射。这里m′和m分别为杂质原子和基质原子的质量;γ′和γ分别为杂质与近邻之间和一般近邻之间的力常数。以同样的模型计算了各种类型声子对杂质中心吸收带宽的贡献。指出,宽度很窄的g型不稳定局域模对带宽的贡献可能变得很大,而超过其余声子的总贡献。最后讨论了单有效频率近似可能有的微观理论基础的问题。As a continuation of our previous work on the (stable) local modes and their effect on the absorption band width of isolated impurity centres, the problem of unstable local modes is considered in this article. By means of the method of group theory, both the unstable local modes and the scattered wave are classified according to the irreducible representations of relevant site group. The case of a simple cubic lattice with nearest neighbour interaction is discussed in detail and the related calculations are carried out. The results show that when a g-type unstable local mode has a rather narrow width, its contribution to the absorption band width may become so large that it exceeds the total contribution of all other lattice vibration waves. Finally, a brief discussion is given on the microscopic basis of the empirical formula of a "single effective frequency" of the electron-phonon coupling.
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