Electrochemical oligomerization mechanism of polyselenophene (PSe) has been studied using hybrid functional B3LYP with the basis set of 6-31G (d). Two different mechanisms - radical-radical (RR) and radical-neutral (RN) couplings - have been assumed to propagate oligomers. The energies concerned with the changes between these stages have been calculated using the optimized geometries and discussed. RR couplings have been concluded to be more favorable than RN couplings due to the high ionization energies of cationic intermediates. Natural Bond Orbital Analysis for each of the optimized structures has been performed to get insight into the nature of the bonds formed in the products along the mechanism path. It was seen that the transition state and intermediate structures could easily be traced by vibrational bands in the related parts. In the second part of the study, the band structure of PSe has been studied employing the same hybrid density functional with periodic boundary conditions.