The ground state and S-wave resonance states of positronium hydride
Z. C. Yan and Y. K. Ho
Phys. Rev. A 59, 2697 (1999)

The fully correlated calculations in Hylleraas coordinates for the nonrelativistic ground-state energy and the first three S-wave resonances of positronium hydride are reported. For the resonances, the positions and widths are determined using the method of complex-coordinate rotation. Our results significantly improve previous work. For example, the ground-state energy is about five parts in 10⁹ in accuracy, the lowest variational upper bound reported to date. A comparison with other previous work is made.