Polarization effects in low-energy electron-CH4 elastic collisions in an exact exchange treatment.

Abstract

We have investigated the polarization effects in very-low-energy (below 1 eV) electron- ${\mathrm{CH}}_{4}$ collisions in an exact-exchange treatment. The two models of the parameter-free polarization potential are employed; one, the ${V}_{\mathrm{pol}{}^{\mathrm{JT}}}$ potential, introduced by Jain and Thompson [J. Phys. B 15, L631 (1982)], is based on an approximate polarized-orbital method, and two, the correlation-polarization potential ${V}_{\mathrm{pol}{}^{\mathrm{CP}}}$, first proposed by O'Connel and Lane [Phys. Rev. A 27, 1893 (1983)], is given as a simple analytic form in terms of the charge density of the target. In this rather very low-energy region, the polarization effects play a decisive role, particularly in creating structure in the differential cross section (DCS) and producing the Ramsauer-Townsend minimum in the total cross section. Our DCS at 0.2, 0.4, and 0.6 eV are compared with recent measurements. We found that a local parameter-free approximation for the polarization potential is quite successful if it is determined under the polarized-orbital-type technique rather than based on the correlation-polarization approach.