Configuration-interaction calculation of the Cue(+) ground state

A configuration-interaction (CI) calculation has confirmed an earlier predi ction of positron binding to neutral copper. The single-centre CI expansion gave a binding energy of 0.003 69 Hartree and a 2 gamma annihilation rate of 0.246 x 10(9) s(-1) The energy and annihilation rate are different from a previous calculation using the fixed-core stochastic variational method ( FCSVM) due to the slow convergence of the CI calculation with respect to th e number of spherical harmonics included in the CI expansion. An extrapolat ion of the CI calculation to the infinite spherical harmonic limit improves the quality of agreement with the earlier FCSVM calculation. The present c alculation highlights the importance of an explicit treatment of the strong electron-positron correlations which are present when positrons interact w ith atoms.