Padé-resummed fourth-order many-body perturbation theory: Applications to the description of Au–Au, Au–Hg, and Hg–Hg bonds

Pilot applications of Padé-resummed fourth-order many-body perturbation theory to the description of chemical bonds with strong contributions from the interactions of filled d-shells (Au–Au, Au–Hg, and Hg–Hg) are reported. The employed Padé approximants, especially the constrained [0/1, 1] quadratic one, ensure radical improvements of accuracy with respect to the partial summation. The non-separability problem is discussed and bypassed through the direct resummation of perturbative expansions for differential correlation energies.