Positron and positronium chemistry by quantum Monte Carlo. IV. Can this method accurately compute observables beyond energy?

Many different properties of the positron containing systems PsH, [Li,e(+)] , LiPs, and [LiH,e(+)], were computed using both variational Monte Carlo an d fixed node diffusion Monte Carlo methods, and explicitly correlated trial wave functions. Our results show that these techniques can accurately comp ute not only energy values, but also other observables. Our [delta(r(+-))] values for PsH, [Li,e(+)], and LiPs are in good agreement with the most rec ent state of the art correlated calculations, while for [LiH,e(+)] our calc ulations are the first to give reliable results. (C) 1999 American Institut e of Physics. [S0021-9606(99)30725-X].