A Systemic DFT Study on Several 5d-Electron Element Dimers: Hf2, Ta2, Re2, W2, and Hg2

Eleven kinds of density functionals in conjunction with three different basis sets are employed to investigate the homonuclear 5d-electron dimers: Hf-2, Ta-2, Re-2, W-2 and Hg-2. The computed bond lengths, vibrational frequencies and dissociation energies of these molecules are used to compare with available experimental data to find the appropriate combination of functional and basis set. The different functionals and basis sets favor different ground electronic state for Hf-2 and Re-2 molecules, indicating that these two dimers are sensitive to the functionals used. The molecular properties of Hg-2 dimer depend strongly on both functionals and basis sets used. It is found that the BP86 and PBEPBE functionals are generally successful in describing the 5d-electron dimers. For the ground states of these dimers, the bonding patterns are determined by natural bond orbital (NBO) analysis. Natural electron configurations show that the 6s and 5d orbitals in the bonding atoms hybrid with each other for the studied dimers except for Hg-2.