Quasi-relativistic study of electronic structure of uranium tetrafluoride

Conclusions A comparison of the results obtained in a calculation of the electronic structure of UF₄, performed in the NR and QR approximations of the X-SW method, leads to a number of conclusions as to the role of relativistic effects in the electronic structure of molecules. a) An accounting for relativistic effects leads to changes in the spatial distribution of charge in the molecules and to a consequent change in the interpretation of the bond in terms of the ratio of ionic and covalent components. b) Relativistic compression of the wave functions of the s and p electrons (primary relativistic effects) and delocalization of the d and f functions (secondary relativistic effects) lead to substantial changes in the orbital energies and the corresponding ionization potentials in heavy molecules. c) Primary and secondary relativistic effects are responsible for considerable changes in the electronic excitation energies and the EA, changes that may account to as much as 200%. d) An accounting for spin-orbit interaction effects is extremely important in interpreting photoelectron and optical spectra. In the example of UF₄, it has been shown that NR wave functions are inadequate for use in calculating spin—orbit splittings in heavy molecules. Just as inadequate may be an accounting for spin—orbit interaction in first-order perturbation theory for systems of closelying MOs, the charge density of which is determined to a considerable degree by AOs of a single type (for example, 5f AOs of uranium in UF₄).Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 20, No. 4, pp. 406–415, July–August, 1984.The authors wish to express their appreciation to M. I. Timokhin for assistance in performing the calculations.