Superheavy atoms and molecules with occupied 5g spinors—Ubh (Z = 126) and UbhF

All-electron fully relativistic calculations, including electron correlation at the 4-component coupled cluster level of theory, have been carried out on the diatomic fluoride of element 126, UbhF, as well as Ubh and Ubh+. Using large Gaussian basis sets at the CCSD(T) level of theory with the Dirac–Coulomb Hamiltonian, the dissociation energy of UbhF is calculated to be 6.95 eV at an equilibrium bond length of 2.030 Å. Compared to its neighbor UbpF (i.e., E126F), the UbhF molecule has a slightly smaller dissociation energy, but its bond length is shorter by nearly 0.04 Å. The ground electronic state of UbhF involves 2 electrons in 5g spinors, which are non-bonding in character, as well as a doubly occupied 8s and partially occupied 8p and 6f spinors. Overall, the Ubh-F bond is ionic with a Mulliken charge of +0.73 e on Ubh. Non-relativistic calculations at the MRCI level of theory indicate that relativity strengthens the UbhF bond by about 0.8 eV. The ionization energy of the Ubh atom, which involves removal of an 8p1/2 electron, is calculated to be 4.95 eV, which is also determined to be strongly increased by relativistic effects.