A simple method for evaluating low-energy electron-molecule scattering cross sections using discrete basis functions

Many-Body Theory Calculations of Positron Scattering and Annihilation in H_{2}, N_{2}, and CH_{4}

The recently developed ab initio many-body theory of positron molecule binding [22J. Hofierka et al., Many-body theory of positron binding to polyatomic molecules, Nature (London) 606, 688 (2022)NATUAS0028-083610.1038/s41586-022-04703-3] is combined with the shifted pseudostates method [A. R. Swann and G. F. Gribakin, Model-potential calculations of positron binding, scattering, and annihilation for atoms and small molecules using a Gaussian basis, Phys. Rev. A 101, 022702 (2020)PLRAAN2469-992610.1103/PhysRevA.101.022702] to calculate positron scattering and annihilation rates on small molecules, namely H_{2}, N_{2}, and CH_{4}. The important effects of positron-molecule correlations are delineated. The method provides uniformly good results for annihilation rates on all the targets, from the simplest (H_{2}, for which only a sole previous calculation agrees with experiment), to larger targets, where high-quality calculations have not been available.

Positron scattering and annihilation from the hydrogen molecule at zero energy

The confined variational method is used to generate a basis of correlated Gaussians to describe the interaction region wave function for positron scattering from the H2 molecule. The scattering length was approximately = -2.7a(0) while the zero energy Z(eff) of 15.7 is compatible with experimental values. The variation of the scattering length and Z(eff) with internuclear distance was surprisingly rapid due to virtual state formation at R approximately = 3.4a(0).