Ab Initio Calculation of Infinite TCNQ and TTF Stacks

The calculations were performed in the second-neighbor interaction approximation and, for the stacked chains, the geometry found in the mixed TCNQ-TTF crystaF (3.18 A interplane distance in the TCNQ stack and 3.47 A in the TTF stack) was applied. The GAUSSIAN 74 program generalized to infinite chains with periodic boundary conditions was used by applying the STO-3G basis set. To attain self-consistency, about 30 iteration steps were needed to fulfill simultaneously the applied SCF criteria  

The numerical integrations necessary to calculate the generalized bond orders P q)rji ( = 0,1,2) involved nine different values of k in the interval Q-nla (according to our previous experience, nine different values of k already give a consistent band structure). 

TABLE 2.5. Valence and Conduction Bands of Poly(TCNQ) and Poly(TTF) and Their 

2 Ab Initio Calculations on Quasl-One-Dinransional Polymers 

This may throw some light on the fact that neither theoretical (ab initio SCF LCAO MO) calculations on a TCNQ-TTF molecule pair with realistic structural data modeling the situation in the mixed crystal nor measurements on aqueous solutions containing both TCNQ and TTF molecules as solutes indicated CT, which seems to be a purely solid-state physical effect in the mixed crystal ( 0.6e per TCNQ-TTF pair).  

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