Computer Physics Communications 136 (2001) 117–125 www.elsevier.nl/locate/cpc Application of the method of continued fractions to electron scattering by polyatomic molecules E.M.S. Ribeiro a , L.E. Machado b , M.-T. Lee c , L.M. Brescansin a,∗ a Instituto de Física Gleb Wataghin, UNICAMP, 13083-970 Campinas, SP, Brazil b Departamento de Física, UFSCar, 13565-905 São Carlos, SP, Brazil c Departamento de Química, UFSCar, 13565-905 São Carlos, SP, Brazil Received 8 July 2000; accepted 7 December 2000 Abstract A new computational code based on the method of continued fractions is developed to study low-energy electron scattering by polyatomic molecules with arbitrary symmetry. As a first application, this code is used to study elastic electron scattering by four representative molecules with different symmetries, viz., H 2 , CH 4 ,H 2 O, and NH 3 . The calculated physical quantities such as reactance  K matrices, differential cross sections, etc, converge rapidly. Also, our calculated cross sections are in good agreement with other available theoretical and/or experimental data, confirming that this is an efficient method for studying electron molecule scattering.  2001 Elsevier Science B.V. All rights reserved. PACS: 34.80.Bm; 02.70.-c; 03.65.Nk Keywords: Polyatomic molecules; Electron scattering; H 2 ; CH 4 ;H 2 O; NH 3 ; Cross sections 1. Introduction The application of the method of continued frac- tions (MCF) to electron-atom scattering was originally proposed by Horᡠcek and Sasakawa in 1983 [1]. In their paper, the l = 0 partial-wave phase shifts for electron scattering by hydrogen atom were success- fully obtained in the static and static-exchange (SE) levels of approximation. Lately, the application of the MCF to multichannel scattering problems was also discussed by several authors [2–4]. Also, numerical tests for the application of the MCF to electron scatter- ing using both local and nonlocal model potentials [2, 5–7] were performed. In all these studies the rapid * Corresponding author. E-mail address: bresca@ifi.unicamp.br (L.M. Brescansin). convergence of the iterative procedure reinforced the adequacy of the MCF for studying electron-atom scat- tering problems. In 1995 the MCF was adapted by Lee et al. [8] to study low-energy electron scattering by neutral and ionic He in the SE approximation, as well as positron scattering by atomic hydrogen in two- and five-channel coupling levels. In the same year this method was also applied to study low-energy elec- tron scattering by linear molecules [9]. Since then the applicability of the MCF to study electron–linear molecules scattering has been systematically extended by our group. For instance, Lee et al. applied the MCF to the calculation of elastic [10] and excita- tion [11] cross sections for electron scattering by H 2 in the low- and intermediate-energy range. Recently, 0010-4655/01/$ – see front matter  2001 Elsevier Science B.V. All rights reserved. PII:S0010-4655(01)00151-5