“…Trans-PA ( Figure 9a) is a prototypical system, probably one of the most studied polymers because of its small size and extreme sensitivity of the predicted bond length alternation (BLA) between single and double bonds with respect to the theoretical method used. The latter has motivated many researchers to apply various available methods to this quite difficult problem [23,28,38,41,104,105,106,107,108,109,110,111,112,113,114,115].…”