Diagrammatic exciton-basis valence-bond theory of linear polyenes
Diagrammatic exciton-basis valence-bond theory of linear polyenes
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DOI：
10.1103/physrevb.59.4822
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发表时间：
1999-02-15
影响因子：
3.7
通讯作者：
Mazumdar, S
中科院分区：
文献类型：
--
作者：
Chandross, M;Shimoi, Y;Mazumdar, S
理解π共轭聚合物的光物理需要对光物理中涉及的激发态的物理理解。详细的物理理解是困难的，因为在这些系统的现实理论模型中发生了广泛的配置相互作用。我们开发了一个图解的激子基价键表示，特别适用于这些系统中库仑相互作用的中等量级。我们提出了精确的激子基处理和以前的近似方法的详细比较，重点放在过去被忽视的特定多体和单粒子相互作用及其后果上。在此基础上，我们给出了十碳线性多烯的非相互作用带极限、孤立二聚体通过库仑相互作用的极限以及具有两种不同键交替参数的parer - parr - people Ohno库仑相互作用的精确数值计算结果。在每种情况下都获得了与光物理相关的本征态的简单图像描述，并且综合起来，这些结果提供了低激发态和高能激发态的系统表征：在线性链π共轭系统中具有实际参数。定义并计算了两个不同的量，即激子基内的有效激发数和单激发本征态的粒子-空穴相关长度，以便进一步定量比较本征态之间的差异。由此得到光学非线性的图形描述。对于小键和大键交替，发现在低能区主导三阶光学非线性的双光子态是最低的偶宇称单激发态，其粒子-空穴相关长度大于1 B-u激子。mA(g)态占主导地位的原因可以从当前算符的性质在激子基础上理解。结果表明，相关mA(g)与相关1B(u)之间的关系与不相关2A(g)与不相关1B -u之间的关系相同。在光谱的高能区域，从单线态-单线态双激发波函数的性质中发现了稳定双激子的证据。
Understanding the photophysics of pi-conjugated polymers requires a physical understanding of the excited states involved in the photophysics. Detailed physical understanding is difficult because of the extensive configuration interaction that occurs within realistic theoretical models fur these systems. We develop a diagrammatic exciton-basis valence-bond representation that is particularly suitable for the intermediate magnitude of the Coulomb interactions in these systems. We present detailed comparisons of our exact exciton-basis treatment and previous approximate approaches, focusing on the specific many-body and single-particle interactions that have been ignored in the past, and the consequences thereof. Following this, we present the results of exact numerical calculations for the noninteracting band limit, the limit of isolated dimers interacting through Coulomb interactions, and for the Pariser-Parr-Pople Ohno Coulomb interactions with two different bond-alternation parameters for the ten-carbon linear polyene. Simple pictorial descriptions of the eigenstates relevant in photophysics an obtained in each case, and taken together, these results provide a systematic characterization of both low- and high-energy excited states: in linear chain pi-conjugated systems for realistic parameters. Two different quantities, the number of effective excitations within the exciton basis, and the particle-hole correlation length for the one-excitation eigenstates are defined and calculated fur further quantitative comparisons between the eigenstates. A pictorial description of optical nonlinearity is obtained thereby. For both small and large bond alternation, it is found that the two-photon state that dominates third order optical nonlinearity in the low-energy region is the lowest even parity one-excitation state with a larger particle-hole correlation length than the 1 B-u exciton. The reason for the dominance by this mA(g) state can be understood within the exciton basis from the nature of the current operator. It is shown that the relationship between the correlated mA(g) and the correlated 1B(u) is identical to that between the uncorrelated 2A(g) and the uncorrelated 1 B-u. In the high-energy region of the spectrum evidence for stable biexcitons is found from the nature of the singlet-singlet two-excitation wave functions.