Ab initio all-electron Dirac–Fock–Breit calculations for ThF4 using relativistic universal Gaussian basis set

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Abstract
Ab initio all‐electron fully relativistic Dirac–Fock–Breit calculations are reported for ThF4 assuming the experimental tetrahedral geometry with the Gaussian nuclear model for the Th and F nuclei. The calculations were performed with our relativistic universal Gaussian basis set, which has been shown to be of Dirac–Fock accuracy for all atoms. The calculated relativistic correction to the total electronic energy of ThF4 is −2150.5 hartrees (−58 518 eV) which is about 9% of its total Hartree–Fock energy. There are also major relativistic corrections to the binding energies of the molecular orbitals, especially for the inner (core) orbitals of ThF4. The magnetic part of the Breit interaction is calculated to be 38.8 hartrees (1056 eV) for ThF4. The results of our ab initio all‐electron relativistic calculations, predict the molecule ThF4 to be bound with respect to dissociation into one Th and four F Dirac–Fock atoms. The dissociation energy predicted by our relativistic calculations for ThF4 of 19.34 eV is 70% of the experimental value (27.7 eV) reported by Lau et al. [J. Chem. Phys. 90, 1158 (1989)]. This result is quite remarkable in view of the fact that it was obtained by using single configuration Dirac–Fock self‐consistent field wave function for the tetrahedral ThF4. Our NR HF calculations for the tetrahedral ThF4 also predict the molecule to be bound with the predicted dissociation energy of 19.11 eV, which is only 0.23 eV less than that predicted by our relativistic wavefunction. Therefore, although the relativistic correction to the total electronic energy of ThF4 is very significant, its contribution to the binding energy of the molecule is almost negligible (0.23 eV). This is due to the cancellation of the relativistic corrections for the ThF4 molecule and its constituent atoms.