Van der Waals coefficients for positronium interactions with atoms

Abstract

The random-phase approximation with exchange (RPAE) is used with a $B$-spline basis to compute dynamic dipole polarizabilities of noble-gas atoms and several other closed-shell atoms (Be, Mg, Ca, Zn, Sr, Cd, and Ba). From these, values of the van der Waals ${C}_{6}$ constants for positronium interactions with these atoms are determined and compared with existing data. After correcting the RPAE polarizabilities to fit the most accurate static polarizability data, our best predictions of ${C}_{6}$ for Ps--noble-gas pairs are expected to be accurate to within 1%, and to within a few percent for the alkaline-earth metals. We also used accurate dynamic dipole polarizabilities from the literature to compute the ${C}_{6}$ coefficients for the alkali-metal atoms. Implications of increased ${C}_{6}$ values for Ps scattering from more polarizable atoms are discussed.