The thermochromatographic registration of superheavy element 112 (E112, Cp, eka-Hg) on gold surface [1] remains the only reliable way of its chemical identification. Experimental data indicate that the E112/Au adsorption energy is rather large (0.5-0.8 eV) and notably exceeds the corresponding value for element 114 (E114), whereas recent relativistic DFT (RDFT) calculations predict that the binding energies between E112 and gold clusters are smaller than the corresponding energies for E114. Moreover, two-component RDFT estimates for E112-Aun binding energies for large n seem to converge to the values well below the range compatible with the experimental data. To check the validity of RDFT methods in application to E112-Au interactions, we estimated the parameters of few E112-Aun systems by combining the results of scalar relativistic many-body perturbation theory calculations with geometry-dependent spin-orbit contributions to interaction energies [2] evaluated at the DFT level (MBPT+SO). The latter contributions are nearly independent on the choice of exchange-correlation functionals (XCFs). All calculations were performed within accurate two-component small-core relativistic pseudopotential model. While a reasonable agreement of relativistic DFT and MBPT+SO results for the bond parameters in the E112Au diatomic is readily achieved with simple gradient or hybrid XCFs, MBPT+SO estimates of E112 - Aun binding energies for Au clusters simulating adsorption sites are found to be systematically much larger than their DFT counterparts. This result can be explained by the peculiarity of the atomic structure of E112 consisting in highly polarizable though still compact filled 6d-shell. This suggests a rather strong dispersion-like interactions of quasi non-overlapping d-shells of E112 and Au, in a sense resembling the aurophilic attraction. DFT approaches with conventional XCFs are not suitable for describing this kind of interactions and seem to fail in this case.
The authors express their gratitude to A.A. Granovsky and C. van Wuellen. The work was partially supported by the Russian Foundation for Basic Research (grants no. 09 03 00655 and 09 03 12255 ofi-m).
1. R. Eichler et al., Nature 447, 72 (2007)
2. A. Zaitsevskii et al., Cent. Eur. J. Phys. 4, 448 (2006)