Positron and positronium interactions with Cu

The configuration-interaction (CI) method is used to investigate the interactions of positrons and positronium with copper at low energies. The calculations were performed within the framework of the fixed-core approximation with semiempirical polarization potentials used to model dynamical interactions between the active particles and the (1s-3d) core. Initially, calculations upon the e⁺Li system were used to refine the numerical procedures and highlighted the extreme difficulties of using an orthodox CI calculation to describe the e⁺ Li system. The positron binding energy of e⁺Cu derived from a CI calculation which included electron and positron orbitals with l<~18 was 0.005 12 hartree while the spin-averaged annihilation rate was 0.507×10⁹s^-1. The configuration basis used for the bound-state calculation was also used as a part of the trial wave function for a Kohn variational calculation of positron-copper scattering. The positron-copper system has a scattering length of about 13.1a₀ and the annihilation parameter Z_eff at threshold was 72.9. The dipole polarizability of the neutral copper ground state was computed and found to be 41.6a₀³. The structure of CuPs was also studied with the CI method and it was found to have a binding energy of 0.0143 hartree and an annihilation rate of ∼2×10⁹s^-1.