Abstract: 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.
...