Communication: Viewing the ground and excited electronic structures of platinum and its ion through the window of relativistic coupled cluster method.

Highly accurate electronic structure calculations are often needed to supplement scant experimental data. We report the ground D and some selected low lying excited/ionized states of Pt and its ions obtained using the Fock space multireference coupled cluster method with four-component relativistic spinors. The present work establishes the stability of the S state of its negative ion and reproduces the binding energy of this state within 10 cm. The first ionization potential (cm) is estimated to be 72 005, deviating from the experiment by just 200 (0.3%). We also report the magnetic hyperfine coupling constants (A) of Pt and its ions. The present calculation provides the A value (GHz) of the D state of Pt to be 5.78 exhibiting very good agreement with the experimental data of 5.70. To our knowledge, this is the first relativistic ab initio calculation of the ionization potential and magnetic hyperfine coupling constant for the neutral and ionic states of Pt at a high level of correlation treatment.