A procedure has been devised to calculate bond order (multiplicity) indices, actual valences as well as one- and two-center energy components from the results of ab initio LCAO-CO calculations of polymers. These quantities permit one a deeper physico-chemical insight into the electronic structure of systems studied. As an example, applications to the band gap opening in a polyacetylene chain are presented and discussed. (C) 2004 Elsevier B.V. All rights reserved.