电荷转移复合分子晶体TMPD·(TCNQ)2的电子能带结构及其与NMP·TCNQ和TTF·TCNQ的比较

本文对电荷转移复合分子晶体TMPD·(TCNQ)_2的电子能带进行了计算。在计算中将TMPD及TCNQ分别作为准一维分子柱来处理。所用计算方法为EHMO/LCAO-MO-CO方法。计算结果再次证实我们在前文给出的规律, 即分子晶体能带的位置由其孤立分子相应分子轨道能级的位置决定, 而能带宽度由相邻分子的相应分子轨道间的相互作用决定。本文还对该晶体的能带结构及其与室温电导率的关系进行了讨论, 并与NMP·TCNQ 和TTF·TCNQ晶体的进行比较。

STRUCTURE OF THE ELECTRONIC ENERGY BANDS OF THE CHARGE TRANSFER COMPLEX MOLECULAR CRYSTAL TMPD·(TCNQ)2 AND THE COMPARISON WITH THOSE OF NMP·TCNQ AND TTF·TCNQ

The electronic energy bands of the charge transfer complex molecular crystal TMPD·(TCNQ)_2 have been calculated. In the calculation,both TMPD and TCNQ are treated as quasi-one-dimensional molecular columns respectively (Figs.1 and 2), and two adjacent molecules are considered as a super-molecule.The method of EHMO/LCAO-MO-CO is used Eqs.(1)—(5)]. According to the principle of super- conjugation, the methyl group in TMPD is treated as a heteroatom Me with seven electrons. The valence orbital ionization potential I_(Me) and orbital exponent ζ_M of the 2p orbital are given in Eqs.(6) and (7). The results of the frontier and subfrontier energy bands and the energy levels of the corresponding orbitals of the respective isolated molecules (E_(iso)) are shown in Tables 1 and 2.From Figs.3 and 4, it can be seen that the energy bands of the molecular column TMPD are quasi-double degenerated to a larger extent than those of the columns NMP and TTF. This is because, in these molecular columns, one supermolecule is composed of two molecules, and the intermolecular distance within the column TMPD is larger than those of columns NMP and TTF. It can also be seen that the band E_(HO) of column TMPD jonts with E_(HO-1) at α=0.5, but the band E_(LU) of column TCNQ in crystal TMPD·(TCNQ)_2 does not connect with E_(LU+1). This fact is concerned with the low electrical conductivty of the crystal....