Bound and resonance states of positronic copper atoms

We report a theoretical calculation for the bound and S-wave resonance states of the positronic copper atom (e⁺Cu). A positron is a positively charged particle; therefore, a positronic atom has an attractive correlation between the positron and electron. A Gaussian expansion method is adopted to directly describe this correlation as well as the strong repulsive interaction with the nucleus. The correlation between the positron and electron is much more important than that between electrons in an analogous system of Cu^-, although the formation of a positronium (Ps) in e⁺Cu is not expressed in the ground state structure explicitly. Resonance states are calculated with a complex scaling method and identified above the first excited state of the copper atom. Resonance states below Ps (n = 2) + Cu⁺ classified to a dipole series show agreement with a simple analytical law. Comparison of the resonance energies and widths of e⁺Cu with those of e⁺K, of which the potential energy of the host atom resembles that of e⁺Cu, reveals that the positions of the resonance for the e⁺Cu dipole series deviate equally from those of e⁺K.