A theoretical benchmark study of the spectroscopic constants of the very heavy rare gas dimers

Abstract

Spectroscopic constants for the homonuclear dimers of the very heavy rare gases radon (Rn) and eka-radon (Uuo) are reported. A computational protocol using the eXact 2-Component molecular-mean field Hamiltonian has been established based on extensive calculations of the xenon dimer. We find that reliable results require CCSD(T) calculations at the extrapolated basis set limit. In this limit counterpoise corrected results are closer to experimentally derived values than uncorrected ones. Furthermore, in an attempt to reduce the computational cost while retaining very high accuracy, we studied the performance of range-separated density functional theory. Although we observe a somewhat more favorable basis set convergence and reduced importance of connected triples by range-separated methods compared to pure wave function theory, in practice we have to employ the same computational protocol for obtaining converged results. At the Dirac-Coulomb level we find an almost fourfold increase of binding energy when going from the radon to the eka-radon dimer, but the inclusion of spin-other orbit interaction reduces the dissociation energy of the heaviest dimer by about 40%.

Toward an accurate description of solid-state properties of superheavy elements

“…We see that the short bond distance for the Og dimer (Table 1) [24] is causing an anomalous behaviour in the trend down the rare gas dimers. This translates directly into an anomaly in the nearest neighbour distances of the rare gas solids down that group.…”

“…This translates directly into an anomaly in the nearest neighbour distances of the rare gas solids down that group. The bond distances r e and binding energies for Rn 2 and Og 2 were taken from relativistic coupled cluster calculations of Saue and co-workers, which include corrections for basis set superposition errors and are extrapolated to the basis set limit [24]. Their perturbative triples contributions to the dissociation energy of the rare gas dimers in the coupled cluster procedure are however rather large indicating that one has to include quadruple corrections as well within the coupled cluster procedure, which becomes computationally demanding.…”

“…Cohesive energies at optimized bond distances (see Table 1) for the rare gas fcc lattices from Ne to Og (Z = 118) using a Lennard-Jones (6-12) potential and a three-body Axilrod-Teller term. Lennard-Jones binding energies -(taken from references [22][23][24][25]) and cohesive energies E coh at various levels of theory (see text). The total ZPE (TZPE) includes both harmonic (HE) and anharmonic terms (AE).…”

Benchmarking density functionals in conjunction withGrimme's dispersion correction for noble gas dimers (Ne2, Ar2, Kr2, Xe2, Rn2)

“…There is extensive literature devoted to Ng 2 dimers (e.g., Refs. and references therein). Ne 2 , Ar 2 , Kr 2 , and Xe 2 have been detected by means of their molecular spectra .…”

Heaviest Element Has Unusual Shell Structure

“…This effect, particularly strong for neutrons, is due to the high density of single-particle orbitals. 118 Og, 0.89 þ1.07 −0.31 ms, is too short for chemical "oneatom-at-a-time" studies; hence, its chemical properties must be inferred from advanced atomic calculations based on relativistic quantum theory [6][7][8][9][10][11][12][13][14][15][16][17][18][19]. According to these, Og has a closed-shell ½Rn 5f 14 6d 10 7s 2 7p 6 configuration [13,20,21], with a very large spin-orbit splitting of the 7p shell (9.920 eV at the Dirac-Breit-Hartree-Fock and 10.125 eV at the Fock-space coupled-cluster level; see below).…”