Electronic and phonon instabilities in face-centered-cubic alkali metals under pressure studied usingab initiocalculations

Abstract

The evolution of Fermi surfaces and lattice dynamics for alkali metals in the fcc structure with pressure have been studied using ab initio calculations within the density functional theory. Fermi surface nesting features along the $\ensuremath{\Gamma}\text{\ensuremath{-}}\mathrm{K}$ symmetry direction in the Brillouin zone have been identified for Li, K, Rb, and Cs, while it is absent for Na. Moreover, a transverse acoustic phonon softening along the $\ensuremath{\Gamma}\text{\ensuremath{-}}\mathrm{K}$ with pressure is predicted for Li, Na, K, Rb, and Cs. This observation suggests a common phonon softening behavior in fcc alkali metals at high pressure. Analysis of the theoretical results suggests that the consideration of both phonon and electronic instabilities is crucial to the understanding of pressure-induced phase transitions in the fcc alkali metals.