Considering the changes of the geometric shielding effect in a molecule as the incident electron energy varies, an empirical fraction, which is dependent on the incident electron energy and the target molecular dimension, is presented. Using this empirical fraction, the total cross section for electron scattering by relatively larger molecule H2S (which contains relatively larger atom, sulfur) and complex polyatomic molecule C2F6 (which contains eight atoms) are calculated over the energy range 30-5000 eV based on the additivity rule model at Hartree-Fock level. The quantitative total cross sections are compared with those obtained by experiments and other theories wherever available, and good agreement is attained. (c) 2006 Elsevier B.V. All rights reserved.