Positron chemistry by quantum Monte Carlo. II. Ground-state of positron-polar molecule complexes

The stability of the ground-state of positron-polar molecule complexes [M,e+] has been explored for M=LiH,HF,H2O,BeO,LiF using variational and diffusion Monte Carlo techniques. Our simulations show that the ground-state of the complexes [LiH,e+]2,1Σ+, [BeO,e+]2,1Σ+, and [LiF,e+]2,1Σ+ is stable against the dissociation either in the two fragments M and e+ or in the other two fragments M+ and Ps=[e+,e−], while the ground-state of [H2O,e+]2,1A1, and of [HF,e+]2,1Σ+ has an energy equal to the dissociation threshold, M and e+. We also compare the predicted vertical positron affinity (PA) with high quality vertical electron affinity (EA) and discuss the relevant difference between the two values.