On the dynamic form factor of an electron liquid

The mean field theories of an electron liquid at metallic densities, which go beyond the RPA, and which have been fairly successful so far, are shown to be inadequate when tested against phenomena involving high frequencies. It is also shown that by making a simple Gaussian ansatz for the imaginery part of the response function, χ″(q,ω), and using the zeroth, the first and the third frequency moments of density spectral function to determine the unknown parameters in χ″(q,ω), it is possible to understand at least semiquantitatively the available experimental information regarding the dynamic form factor. Implications of the present analysis as regards the further refinement of the present theories are indicated.