All-electron X(alpha) self-consistent-field calculations of relativistic effects in the molecular properties of Tl-2, Pb-2, and Bi-2 molecules

Relativistic effects in the binding energy, the bond length, and vibrational frequencies of ground-state potential-energy curves are investigated for Tl-2,Pb-2, and Bi-2 by performing relativistic and nonrelativistic all-electron Dirac-Fock-Slater X(alpha) calculations. Wave functions from numerical solutions of Dirac(Hartree)-Fock-Slater equations for atoms are taken as basis sets. A variationally consistent approximation for the direct Coulomb potential has been used for efficiently obtaining accurate potential energy curves. Our calculations confirm that the spin-orbit effect weakens the binding of the 6p-element molecules Tl-2, Pb-2, and Bi-2.