First-Principles Calculation of the Structure of Mercury

Mercury has perhaps the strangest behavior of any of the metals. Although the other metals in column IIB have an $hcp$ ground state, mercury's ground state is the body centered tetragonal $\beta$Hg phase. The most common phase of mercury is the rhombohedral $\alpha$Hg phase, which is stable from 79K to the melting point and meta-stable below 79K. Another rhombohedral phase, $\gamma$Hg, is believed to exist at low temperatures. First-principles calculations are used to study the energetics of the various phases of mercury. Even when partial spin-orbit effects are included, the calculations indicate that the hexagonal close packed structure is the ground state. It is suggested that a better treatment of the spin-orbit interaction might alter this result.