Calculation of positron binding to silver and gold atoms - art. no. 042504

Positron binding to silver and gold atoms was studied using a fully ab init io relativistic method, which combines the configuration-interaction method with many-body perturbation theory. It was found that the silver atom form s a bound state with a positron with binding energy 123 (+/-30%) meV, while the gold atom cannot bind a positron. Our calculations reveal the importan ce of the relativistic effects for positron binding to heavy atoms. The rol e of these effects was studied by varying the value of the fine-structure c onstant alpha. In the nonrelativistic limit, alpha=0, both systems e(+)Ag a nd e(+)Au are bound with binding energies of about 200 meV for e(+)Ag and 2 20 meV for e(+)Au. Relativistic corrections for a negative ion are essentia lly different from that for a positron interacting with an atom. Therefore the calculation of electron affinities cannot serve as a test of the method used for positron binding in the nonrelativistic case. However, it is stil l a good test of the relativistic calculations. Our calculated electron aff inities for silver (1.327 eV) and gold (2.307 eV) atoms are in very good ag reement with corresponding experimental values (1.303 and 2.309 eV, respect ively).