Spin−Orbit and Electron Correlation Effects on the Structure of EF₃ (E = I, At, and Element 117)

Abstract

Structures and vibrational frequencies of group 17 fluorides EF3 (E = I, At, and element 117) are calculated at the density functional theory (DFT) level of theory using relativistic effective core potentials (RECPs) with and without spin-orbit terms in order to investigate the effects of spin-orbit interactions and electron correlations on the structures and vibrational frequencies of EF3. Various tests imply that spin-orbit and electron correlation effects estimated presently from Hartree-Fock (HF) and DFT calculations with RECPs with and without spin-orbit terms are quite reasonable. Spin-orbit and electron correlation effects generally increase bond lengths and/or angles in both C2v and D3h structures. For IF3, the C2v structure is a global minimum, and the D3h structure is a second-order saddle point in both HF and DFT calculations with and without spin-orbit interactions. Spin-orbit effects for IF3 are negligible in comparison to electron correlation effects. The D3h global minimum is the only minimum structure for (117)F3 in all RECP calculations, and the C2v structure is neither a local minimum nor a saddle point. In the case of AtF3, the C2v structure is found to be a local minimum in all RECP calculations without spin-orbit terms, and the D3h structure becomes a local minimum at the DFT level of theory with and without spin-orbit interactions. In the HF calculation with spin-orbit terms, the D3h structure of AtF3 is a second-order saddle point. AtF3 is a borderline case between the valence-shell-electron-pair-repulsion (VSEPR) structure of IF3 and the non-VSEPR structure of (117)F3. Relativistic effects, including scalar relativistic and spin-orbit effects, and electron correlation effects together or separately stabilize the D3h structures more than the C2v structures. As a result, one may suggest that the VSEPR predictions agree very well with the structures optimized by the nonrelativistic HF level of theory even for heavy-atom molecules but not so well with those from more elaborate theoretical methods. Vibrational frequencies of AtF3 and (117)F3 are modified substantially and nonadditively by spin-orbit and electron correlation contributions. This is one of those rare cases for which vibrational frequencies of the closed-shell molecules are significantly affected by spin-orbit interactions. Spin-orbit interactions decrease all vibrational frequencies of EF3 molecules considered.

The bonding picture in hypervalent XF3 (X = Cl, Br, I, At) fluorides revisited with quantum chemical topology

“…Note that no significant SOC effects were found on the bonding picture whatever the considered XF 3 system. Hence, we have demonstrated that the existence of a stable D 3h structure for AtF 3 is fully compliant with the VSEPR principles, in contrast to preceding claims . We believe that the uncovered mechanism is augmented in the heavier analog, TsF 3 , where only the planar D 3h structure is a minimum .…”

Symmetry exploitation in closed-shell coupled-cluster theory with spin-orbit coupling

“…However, relativistic effects and electron correlation would result in a stable planar D 3h structure for AtF 3 . 55,56 A recent study 57 based on density functional theory 58 including spin-orbit coupling using relativistic ECP indicates that the D 3h structure is the global minimum with most functionals. However, their SR-CCSD(T) results shows that the C 2v structure is actually lower in energy.…”

“…However, their SR-CCSD(T) results shows that the C 2v structure is actually lower in energy. 57 SO-CCSD(T) calculations are thus invaluable to clarify the structure of the global minimum for AtF 3 . We use the ECP60MDF potential 59 and the Def2-QZVPP basis set 50 augmented with several steep p and d functions 45 for At and the cc-pVQZ basis set 54 for F in our calculations.…”

Relativistic and quantum electrodynamic effects in superheavy elements

“…Otherwise 118 is expected to behave just like the other rare gases. First estimates for the adsorption energy of 118 on gold shows that it fits roughly into the series of the rare gas elements [153,165]. However, the dissociation energy of the 118 dimer is predicted to be by a factor of four higher than for Rn 2 , and therefore has the highest dissociation energy within the rare-gas group [166,167].…”