Matter-positronium interaction: A study of the He-atom-positronium system

(Received 29 February 2012; published 16 May 2012)The many-body system comprising a He nucleus, three electrons, and a positron has been studied using anexplicitly correlated Gaussians basis and a stochastic variational method for the optimization of the basis. Thepurpose has been to clarify to which extent the system can be considered as a distinguishable positronium (Ps)atom interacting with a He atom and, thereby, to pave the way to a practical atomistic modeling of Ps states andannihilation in matter. The maximum value of the distance between the positron and the nucleus is constrainedand the Ps atom at different distances from the nucleus is identified from the electron and positron densities,as well as from the electron-positron distance and center-of-mass distributions. The polarization of the Ps atomincreasesasitsdistancefromthenucleusdecreases.ThecontactdensityoftheelectronsofHewiththepositronisdepleted, particularly when the overlap is small. The ortho-Ps pick-off annihilation rate calculated as the overlapof the positron and the free He electron densities has to be corrected for the observed depletion, especially atlarge pores or voids.DOI: 10.1103/PhysRevA.85.052707 PACS number(s): 34 .80.Lx, 31.15.ac, 36.10.Dr