Spin-orbit effects in structural and electronic properties for the solid state of the group-14 elements from carbon to superheavy element 114

Spin-orbit effects approximately scale like Z² and therefore become very important in the bonding of the heavier p -group elements in the periodic table. Here we show by first-principles density-functional calculations that such effects substantially lower the cohesive energy for solid lead and Uuq (ununquadium, eka-lead, nuclear charge 114), by 2.5 eV/atom for the latter and causing a structural change from face-centered cubic at the scalar relativistic to hexagonal close packed at the spin-orbit coupled level of theory. This implies that unlike lead (cohesive energy E_coh=2.02eV/atom ), Uuq is weakly bound (E_coh=0.5eV/atom) , and even less so than solid mercury (E_coh=0.7eV/atom) , underpinning the original hypothesis by Pitzer in 1975 [K. Pitzer, J. Chem. Phys. 63, 1033 (1975)10.1063/1.431398] that spin-orbit effects lead to chemical inertness of Uuq.