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 Ecoh=2.02 eV/atom), Uuq is weakly bound (Ecoh=0.5 eV/atom), and even less so than solid mercury (Ecoh=0.7 eV/atom), underpinning the original hypothesis by Pitzer in 1975 [K. Pitzer, J. Chem. Phys. 63, 1033 (1975)] that spin-orbit effects lead to chemical inertness of Uuq.