Relativistic effects on the electronic structure and chemical bonding of UF6

Abstract

We have studied the relativistic effects in the electronic structure and chemical bonding for the ground state of UF6, using the relativistic and nonrelativistic discrete-variational Xα molecular orbital calculations. It is found that two relativistic effects appear in the valence levels; the energy level splitting and upward shift of energies of the molecular orbitals. From the Mulliken population analysis of the valence levels, it is shown that the level splitting is due to mixing of the uranium atomic orbitals with a strong spin–orbit interaction, such as U6p, and the upward shift due to the increase in the screening of the nuclear charge and charge redistribution. The strength of U–F bonding remarkably increases for the relativistic case, because the changes in the radial distributions due to the relativistic effects induce both the decrease in the antibonding interactions and the increase in the bonding ones.

Relativistic Density – Functional Study of Nuclear Fuels

“…The molecular orbitals (MOs) are obtained by taking a linear combination of atomic orbitals (AOs). Details of the R-DFT method have been described elsewhere (Rosen et al, 1975, Onoe et al, 1993.…”

“…5. Non-relativistic and relativistic one-electron energies for the ground state of UF 6 [Onoe et al, (1993)] As shown in Fig. 5, two kinds of relativistic effects appear in the valence electronic structure: the energy splitting for several MOs and the upward or downward shift in the one-electron energy for individual MOs.…”

“…To understand how the relativistic effects influence the chemical bonding of UF 6 , we have investigated the contribution of individual AOs to the chemical bonding by examining the non-relativistic and relativistic radial wave functions [Onoe et al, 1993]. Figure 6 shows the radial wave functions of the uranium valence atomic orbitals (5f, 6s, 6p, 6d) obtained using non-relativistic and relativistic density-functional calculations.…”

“…6. Non-relativistic and relativistic radial wave functions [R(r)] of U valence atomic orbitals: (a) U5f, (b) U6s, (c) U6p, and U6d [Onoe et al, (1993)] www.intechopen.com…”

“…Table 1. The overlap populations between U and F valence AOs for non-relativistic and relativistic calculations, along with the U-F bond overlap population [Onoe et al, (1993)] 4. Application to assign the valence X-ray photoelectron spectra of uranium metal and compounds Figure 7 shows the experimental valence XPS spectra of UC (Ejima, et al, 1993) (a) and theoretical spectra for the UC 6 (b), CU 6 (c), and CU 6 C 18 (d) cluster models shown in Fig.…”