Correlation-Polarization Effects in Electron/Positron Scattering from Acetylene: A Comparison of Computational Models

TL;DR

This study compares various computational models for low-energy electron and positron scattering off acetylene, highlighting the importance of correlation-polarization effects and evaluating the accuracy of different theoretical approaches against experimental data.

Contribution

It systematically assesses the effectiveness of static, polarization, DFT, DPM, and R-matrix models in predicting scattering cross sections, emphasizing the role of correlation-polarization effects.

Findings

Correlation-polarization effects are crucial for accurate low-energy cross sections.

DFT and DPM models agree well with experimental measurements.

R-matrix results show slower convergence and less agreement with data.

Abstract

Different computational methods are employed to evaluate elastic (rotationally summed) integral and differential cross sections for low energy (below about 10 eV) positron scattering off gas-phase C$_2$H$_2$ molecules. The computations are carried out at the static and static-plus-polarization levels for describing the interaction forces and the correlation-polarization contributions are found to be an essential component for the correct description of low-energy cross section behavior. The local model potentials derived from density functional theory (DFT) and from the distributed positron model (DPM) are found to produce very high-quality agreement with existing measurements. On the other hand, the less satisfactory agreement between the R-matrix (RM) results and measured data shows the effects of the slow convergence rate of configuration-interaction (CI) expansion methods with respect to the size of the CI-expansion. To contrast the positron scattering findings, results for electron-C$_2$H$_2$ integral and differential cross sections, calculated with both a DFT model potential and the R-matrix method, are compared and analysed around the shape resonance energy region and found to produce better internal agreement.