Ab initio pseudopotential calculation for TTF-TCNQ and TSeF-TCNQ

We have investigated the electronic structure of I:he quasi-one-dimensional organic conductor TTF-TCNQ [at room temperature (RT) and 100 K] and TSeF-TCNQ (RT); which have isomorphic crystal structure, by an ab initio plane-wave pseudopotential band calculation. To express the exchange and correlation energy for electrons, we used both the local density approximation and generalized gradient approximation for comparison. For each case, electronic band dispersions were calculated along several symmetric lines and tight-binding parameters were evaluated. The Fermi surface shape was also obtained. The six sets of results (for three structures and two approximations) were compared systematically.