A diffusion Monte Carlo accurate interaction potential between H and PsH

The interaction potential between H and PsH, and between H and H- have been calculated using the diffusion Monte Carlo method. As far as the H-H- syst em is concerned, our results appear to be the most accurate published so fa r. The potential functions show the H-PsH system to be bound with respect t o the H-2+Ps dissociation channel for nuclear distances larger than 3.5 boh r, while the H-2(-)-e(+) threshold lies 0.25 hartree above for all the dist ances studied. Moreover, the H-PsH potential curve presents a minimum locat ed at 5.2 bohr that can be attributed to the van der Waals interaction betw een the two fragments. The relevancy of these results for the low energy sc attering of Ps on H-2 and for the exchange reaction of H with Ps is discuss ed. (C) 2000 American Institute of Physics. [S0021-9606(00)31303-4].