Positronium scattering by lithium

We report cross sections for Ps(1s)-Li(2s) scattering in the energy range up to 30 eV. The calculations have been carried out in a coupled state approximation. The Ps states consist of both eigenstates and pseudostates, the latter to allow for ionization of the Ps. The atom is treated as a frozen core represented by a model potential which supports the valence orbitals. The coupled state expansion includes only the 2s and 2p states of the atom as well as an unphysical 1s state which exists in the model potential. The inclusion of this 1s state is necessary in order to avoid pronounced false pseudostructure. Results are presented for excitation and ionization of the Ps as well as collisions in which the Ps(1s) remains unchanged. These results also differentiate between the case where the Li(2s) remains unexcited and where it is excited to the 2p level.