Relativistic effects on interactions between heavy atoms: the HgHg potential

A quantitative study is made of the magnitude of relativistic effects on the HgHg potential at short and intermediate distances. The interaction potentials in the non-relativistic and relativistic frameworks are calculated by the GordonKim method using relativistic DiracFock densities in the latter case. Large differences are found between the relativistic and the non-relativistic potential (e.g. the relativistic well depth is ≈ 45% of the non-relativistic one). Relativistic corrections to the functional form of the GordonKim energy expression are also examined and found insignificant. General implications of these results to the study of relativistic effects on intermolecular forces are discussed.