Towards first-principles understanding of the metal-insulator transition in fluid alkali metals.

By treating the electron-ion interaction as a perturbation in the first-principles Hamiltonian, we have calculated the density response functions of a fluid alkali metal to find an interesting charge instability due to anomalous electronic density fluctuations occurring at some finite wavevector Q in a dilute fluid phase above the liquid-gas critical point. Since |Q| is smaller than the diameter of the Fermi surface, this instability necessarily impedes the electric conduction, implying its close relevance to the metal-insulator transition in fluid alkali metals.