Ps-Ps scattering via the correlated Gaussian hyperspherical method

There is renewed interest in systems of electrons and positrons since it may be possible to create a Bose-Einstein condensate of spin-triplet positronium atoms [P. M. Platzman and A. P. Mills, Jr., Phys. Rev. B {\bf 49}, 454 (1994)]. We study the four-body system consisting of two positrons and two electrons. Using a basis of correlated Gaussians at fixed hyperradius, we utilize a new technique [K. M. Daily and C. H. Greene, Phys. Rev. A {\bf 89}, 012503 (2014)] to efficiently calculate the adiabatic potentials and non-adiabatic couplings as a function of the hyperradius. The R-matrix is propagated to large hyperradius and scattering properties are derived.