S-wave Ps-Li and Ps-Na scattering

Projectile-elastic, target-elastic, and full close-coupling approximation models have been employed to investigate scattering of ortho-positronium off Li and Na atoms at low energies. Nine different basis sets for each system have been used to find the relative importance of atomic (target and projectile) states on the elastic scattering parameters and the convergence of the predicted results with added eigen- and pseudostates. The s-wave elastic phase shifts, scattering lengths and cross sections of both the systems are reported upto the incident energy k=0.5 a.u. and compared with the corresponding existing theoretical predictions. It has been found that the van der Waals and higher order long-range interactions play a crucial role in predicting s-wave elastic parameters for Ps-alkali-metal-atom systems at low energies