摘要
本文采用以EHMO为基础的紧束缚近似方法计算了同分异构复合物1-N-Mci TCNQ_2和2-N-Mci TCNQ_2的能带结构。通过计算谐振稳定能估算复合物中TCNQ的电荷。计算结果表明,复合物晶体中的给体N-Mci对一维能带的前沿轨道无影响。1-N-Mci和2-N-Mci的几何形状不同,在晶体堆积能量上影响TCNQ的排列,使两个复合物的TCNQ堆积方式不同,能带结构也就不一样了。1-N-Mci TCNQ_2复合物的TCNQ之间π-π轨道迭合较好,能隙小。LU带色散大,LU轨道上的电子为末充满状态(δ≈1.77),具有较好的导电性能。2-N-Mci TCNQ_2复合物中TCNQ二聚体之间π-π轨道重叠不好,能隙大,LU带宽很窄,LU轨道上电子为半充满状态(δ≈1.0),易于形成磁绝缘体,其导电性比1-N-Mci TCNQ_2差,这与实验结果是一致的。
The band structures of two isomeric complexes 1-N-Mci TCNQ_2 and 2-N-Mci TCNQ_2 are calculated with the tight-binding approximation based on the extended Hckle method. The negative charges of TCNQ species in both complexes are estimated by calculating harmonic oscillator stabilization energy with using their geometry directly. The results show that the donor N-Mci has no effect on the front orhitals of band structure in one-dimensional systems. The geometry of 1-N-Mci is different from 2-N-Mci, which concerns with the crystal packing energy and effects on the arrangement of TCNQ species. Consequently, there are the different packing modes of TCNQ species and the different band structures. In 1-N-Mci TCNQ_2 complexe the π-π orbitals overlap is large, so the band gap between the valence band and the lowest empty band is small, and the band spread of the LU band is large. The LU band is partially fulled (δ= 1.77). So 1-N-Mci TCNQ_2 complex has good conductivity. In the 2-N-Mci TCNQ_2 complex the π-π orbitals overlap between TCNQ dimer is small. The band gap is large, and the LU band is narrow. The LU band is nearly half fulled (δ= 1.0). Therefore, 2-N-Mci TCNQ_2 complex may become magnetic insulator. Its conductivity is poorer than 1-N-Mci TCNQ_2, which is agreement with the experimental result.
出处
《物理化学学报》
SCIE
CAS
CSCD
北大核心
1989年第1期50-55,共6页
Acta Physico-Chimica Sinica
基金
中国科学院院内基金R850434
