Theoretical results for the positronium (Ps) formation from hydrogen negative ion, H-, targets are presented. An exact analytical expression is constructed for the transition matrix for Ps formation in collisions of positrons with H- in the framework of Born approximation using three different target wave functions. The corresponding differential and total cross sections are presented for Ps formation in ground state. Comparison between these cross sections for different wave functions reveals the dependence of the Ps-formation process on the choice of the target wavefunction and the effect of correlation among the target electrons on the process.
