Quantization of the dipole moment and of the end charges in push-pull polymers.
Quantization of the dipole moment and of the end charges in push-pull polymers.
复制标题
推拉聚合物中偶极矩和端电荷的量子化。
DOI：
10.1063/1.2799514
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
R. Resta
中科院分区：
文献类型：
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作者：
K. Kudin;R. Car;R. Resta
提出并证明了拟一维立体正则链中端电荷量子化的一个定理。它是物理学中著名的表面电荷定理的直接类比。该定理陈述如下：(1)无论端基如何，在具有中心对称体的立体规则低聚物中，端电荷只能是12的倍数，在长链的极限下，每个单体的纵向偶极矩p只能是单位长度a的12倍。(2)在非中心对称体的低聚物中，末端电荷可以根据体的性质设定为任意值。然而，通过改变端群，人们只能改变端电荷一个整数和偶极矩p一个单位长度a的整数倍。(3)当系统的整个体部分被改变时，端电荷可以任意改变；然而，如果经过这样的修改，系统仍然是中心对称的，那么作为(1)的直接结果，末端电荷只能改变12倍。以上陈述表明，在所有情况下，结束电荷都是唯一确定的，对整数取模，仅由体积的性质决定。该定理的起源是一个与Berry相相关的鲁棒拓扑现象。量化效应首先在玩具liff链中得到证明，然后在一系列具有中性和电荷转移端基的反式聚乙炔低聚物中得到证明。
A theorem for end-charge quantization in quasi-one-dimensional stereoregular chains is formulated and proved. It is a direct analog of the well-known theorem for surface charges in physics. The theorem states the following: (1) Regardless of the end groups, in stereoregular oligomers with a centrosymmetric bulk, the end charges can only be a multiple of 12 and the longitudinal dipole moment per monomer p can only be a multiple of 12 times the unit length a in the limit of long chains. (2) In oligomers with a noncentrosymmetric bulk, the end charges can assume any value set by the nature of the bulk. Nonetheless, by modifying the end groups, one can only change the end charge by an integer and the dipole moment p by an integer multiple of the unit length a. (3) When the entire bulk part of the system is modified, the end charges may change in an arbitrary way; however, if upon such a modification the system remains centrosymmetric, the end charges can only change by multiples of 12 as a direct consequence of (1). The above statements imply that-in all cases-the end charges are uniquely determined, modulo an integer, by a property of the bulk alone. The theorem's origin is a robust topological phenomenon related to the Berry phase. The effects of the quantization are first demonstrated in toy LiF chains and then in a series of trans-polyacetylene oligomers with neutral and charge-transfer end groups.