The ground-state potential energy curve of the radium dimer from relativistic coupled cluster calculations

The potential energy curve for the ground-state of radium dimer (Ra<inf>2</inf>) is provided by means of atomic and molecular relativistic coupled cluster calculations. The short-range part of this curve is defined by an equilibrium bond length of 5.324 Å, a dissociation energy of 897 cm^-1, and a harmonic vibrational frequency of 20.5 cm^-1. The asymptotic behavior at large interatomic distances is characterized by the van der Waals coefficients C<inf>6</inf> = 5.090 × 10³, C<inf>8</inf> = 6.978 × 10⁵, and C<inf>10</inf> = 8.786 × 10⁷ atomic units. The two regions are matched in an analytical potential to provide a convenient representation for use in further calculations, for instance, to model cold collisions between radium atoms. This might become relevant in future experiments on ultracold, optically trapped, radioactive radium atoms that are used to search for a permanent electric dipole moment.