The energy levels of the TSeF molecule have been calculated by the scattered wave method and compared with the experimental photoemission spectrum for TSeF vapor. There is good overall agreement between theory and experiment. Scattered wave calculations for model TSeF dimers lead to a value of 0.59 eV for the infinite stack bandwidth for the TSeF stack in crystalline TSeF-TCNQ (compare with our earlier values of 0.47 eV for TTF and 0.58 eV for TCNQ bandwidths in TTF-TCNQ). The dependence of the bandwidth on stacking distance is also reported for TTF-TCNQ and TSeF-TCNQ. © 1977 IOP Publishing Ltd.