van der Waals coefficients for positronium interactions with atoms

TL;DR

This paper calculates van der Waals coefficients for positronium interactions with various atoms using RPAE, providing highly accurate $C_6$ values that improve understanding of Ps scattering and interactions.

Contribution

It introduces a method using RPAE with B-splines to accurately compute $C_6$ coefficients for positronium-atom interactions, including noble gases and alkaline earths.

Findings

$C_6$ for Ps--noble-gas pairs accurate to within 1%

$C_6$ for alkaline earths accurate to a few percent

Increased $C_6$ implies stronger Ps scattering from polarizable 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. Our best predictions of $C_6$ for Ps--noble-gas pairs are expected to be accurate to within 1%, and to within a few per cent for the alkaline earths. 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.