Ab Initio Fully Relativistic Dirac-Fock Self-Consistent Field Calculations for Compounds of the Translawrencium Elements

Research Objectives

Our goal is to investigate the effects of relativity in atomic and molecular structure, physical and chemical properties, bonding, volatility dissociation energy, and covalency for the superheavy translawrencium elements and their lighter homologs.

Computational Approach

We used our relativistic self-consistent field (SCF) formalism for molecules, with our universal Gaussian basis sets, using the MOLFDIR code assuming a finite Gaussian nuclear model to perform ab initio all-electron fully relativistic Dirac-Fock (DF) and nonrelativistic Hartree-Fock (NR HF) SCF calculations for a large number of molecules of the translawrencium elements. We used the Cray C-90 at NERSC for the evaluation of billions of matrix elements. We performed matrix diagonalization for the SCF part of our DF calculations.

Accomplishments

1. We optimized the bond distance for tetrachlorides of rutherfordium and its lighter homologs, assuming tetrahedral geometry, by performing calculations at four bond distances and by fitting the results to a polynomial.

2. We optimized the bond distances in hexachlorides of seaborgium, tungsten, and molybdenum, assuming octahedral geometry, and we predict that SgCl₆ is the most stable of the hexachlorides of the group 6 elements.

3. We performed the first all-electron fully relativistic DF as well as NR HF SCF calculations on seaborgium hexabromide SgBr₆, which has 316 electrons, assuming octahedral geometry. We optimized the bond distance by performing NR HF SCF calculations at four internuclear Sg-Br separations and fitting the results to a polynomial.

4. We performed calculations for pentachlorides of hahnium, tantium, and niobium, assuming a trigonal bipyramidal geometry.

5. We performed ab initio DF SCF calculations on hassium tetroxide HsO₄.

6. We performed the first ab initio all-electron DF and HF SCF calculations for a number of molecular systems of E112.

Significance

We have investigated the relativistic effects for systems involving superheavy elements and developed a groundwork for inclusion of the next most significant effects due to electron correlation, starting from our DF SCF calculations. Electron correlation effects are very significant for such systems with hundreds of electrons, and cannot be neglected in any accurate prediction of the physical and chemical properties of these systems.

Publications

G. L. Malli 1997. Ab initio Relativistic Quantum Chemistry of Superheavy Transactinides Elements: Rutherfordium through Eka-astatine. Proceedings of the Welch Foundation Conference on Chemical Research XXXXI The Transactinide Elements, Houston, Texas, October 27-28.

G. L. Malli 1997. Ab initio All-electron Fully Relativistic Dirac-Fock-Breit Calculations for the compounds of the Heaviest Elements: The Transactinides Rutherfordium through Eka-Astatine (Z=117), Invited talk, Fourth Workshop on the Physics and Chemistry of the Heaviest Elements, Stenungsund, Goteborg, Sweden, June 5-9.

G. L. Malli and J. Styszynski 1996. Ab initio all-electron Dirac-Fock-Breit calculations for UF6, J. Chem. Phys, 104:1012.

Left: Dirac-Fock total energies for octahedral SgCl₆ at various Sg-Cl bond distances.
Right: Total Dirac-Fock energy of Hassium tetroxide (Td) at various Hs-O distances.