Improving the wavefunction of the Schwinger multichannel method: application for positron elastic scattering by He atom

In the present paper, we propose a development to the Schwinger multichannel (SMC) method (Germano and Lima 1993 Phys. Rev. 47 3976) for the elastic scattering of positrons by targets of arbitrary geometry. The essence of this work is based on the fact that the main limitation of the SMC method resides on what makes it a general method, i.e. the expansion of the scattering function is done in a L2 basis (Cartesian Gaussian functions) and this is very effective only for short range potentials. Our effort now is to improve the SMC through the use of plane waves as trial functions (SMC-PW). In order to do this, we have to evaluate reliable codes involving matrix elements which are a straightforward modification of the SMC method. We also discuss a mechanism for the Buckingham potential (polarization effects) where the cutoff parameter is adjustable to the positronium formation threshold. Our results to positron-He illustrate convergence characteristics for several incident positron energies