We report methodological improvements to the Schwinger multichannel method in the static plus polarization (SP) approximation for low-energy positron-molecule scattering. The enhancements include the use of $f$-type Gaussian functions in the basis sets for both the positron and target molecules, as well as a refined placement of chargeless extra centers to better describe short-range positron-electron interactions. Annihilation parameters $Z_{\text{eff}}$ are calculated both directly and with enhancement factors to assess the role of correlation effects beyond the SP approximation. The improved approach is applied to positron scattering from hydrogen molecule, nitrogen molecule, methane, acetylene, and ethylene, resulting in cross sections and bound-state energies showing improved agreement with recent experimental and theoretical data.

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• Atomic & molecular collisions
• Electron & positron scattering