Anisotropy of thermal expansion and electronic topological transitions in Zn and Cd under pressure

Using first-principles local-density electronic structure calculations we investigate the evolution of the Fermi surface of hcp Zn and Cd under hydrostatic pressure. We find a sequence of electronic topological transitions (ETT) and a region of pressure where several of these ETT's almost coincide, which apparently leads to the experimentally observed anomalies in their lattice parameters. A change of sign of the anisotropic thermal expansion is predicted in this critical region for temperatures below the Debye temperature.