中性多烯自由基中的自旋分布：用密度矩阵重整化群方法研究的巴黎-帕尔-波普尔模型

Spin distribution in neutral polyene radicals: Pariser-Parr-Pople model studied with the density matrix renormalization group method.

作者信息

Ma Haibo, Cai Fei, Liu Chungen, Jiang Yuansheng

机构信息

Institute of Theoretical and Computational Chemistry, Key Laboratory of Mesoscopic Chemistry, Department of Chemistry, Nanjing University, Nanjing 210093, China.

出版信息

J Chem Phys. 2005 Mar 8;122(10):104909. doi: 10.1063/1.1861875.

DOI:10.1063/1.1861875

PMID:15836360

Abstract

The geometries and pi electron spin distributions induced by neutral soliton defects in trans-polyacetylene radicals (from C(7)H(9) to C(49)H(51)) are studied using Pariser-Parr-Pople (PPP) model, solved by the density matrix renormalization group (DMRG) method. Comparisons with other quantum chemical methods as well as the experimental observations on heptatrienyl (C(7)H(9)) and nonatetraenyl (C(9)H(11)) radical species show that the semiempirical PPP method is in the list of the very few theories that can give correct description of the spin distributions for such extended pi-conjugated systems. By virtue of DMRG's power in dealing with large one-dimensional systems, we predicted that the half-width of a neutral spin soliton in polyacetylene is about 14 atoms, and the spin distributions in the center of the soliton is calculated as rho(0)=0.25, rho(1)=-0.12 with rho(1)rho(0)=-0.48, rho(-)rho(+)=-0.52, which agree well with the results from electron-nuclear double resonance experiments.

摘要

利用由密度矩阵重整化群（DMRG）方法求解的巴黎-帕尔-波普尔（PPP）模型，研究了反式聚乙炔自由基（从C(7)H(9)到C(49)H(51)）中中性孤子缺陷诱导的几何结构和π电子自旋分布。与其他量子化学方法以及对庚三烯基（C(7)H(9)）和壬四烯基（C(9)H(11)）自由基物种的实验观测结果的比较表明，半经验PPP方法是极少数能够正确描述此类扩展π共轭体系自旋分布的理论之一。借助DMRG处理大型一维体系的能力，我们预测聚乙炔中中性自旋孤子的半高宽约为14个原子，并且孤子中心的自旋分布计算结果为ρ(0)=0.25，ρ(1)= -0.12，其中ρ(1)/ρ(0)= -0.48，ρ(-)/ρ(+)= -0.52，这与电子-核双共振实验结果吻合良好。