Abstract: Tightly binding calculations have been performed on the linear screw chain as well as the three dimensional lattice of trigonal selenium. Energy bands can be classified into three sets, namely bonding, nonbonding (lone pair bands) and anti- bonding which have been analyzed in terms of space symmetry. In order to eluci- date the bonding analogy inherent in both the lattice and its finite fragment, a hy- pothetical ring cluster with formula Se_6 is elected and investigated by means of EH program in addition. Parallel to COOP introduced by Hughbanks and Hoffmann, a similar quantity-clusterorbital orverlap population is defined which qualitatively estimates the bonding extent between a pair of atoms distributed in the neighborhood of a fixed energy value. Much like results as drawing in curves of energy bands, density of states and COOP have been shown between the lattice and the hypothetical cluster. This reveals to believe that quite similar electron behaviors exist in this kind of solid and the appropriate finite molecule.