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 ${Z}^{2}$ 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 ${E}_{coh}=2.02\text{ }\text{eV}/\text{atom}$), Uuq is weakly bound $({E}_{coh}=0.5\text{ }\text{eV}/\text{atom})$, and even less so than solid mercury $({E}_{coh}=0.7\text{ }\text{eV}/\text{atom})$, 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.