ON THE COLLISIONAL ONE-COMPONENT PLASMA DIELECTRIC FUNCTION

[EN] Asymptotic properties of the collisional one-component plasma dielectric function in the random-phase (RPA) and Mermin approximation, with a constant collision frequency, are analyzed from the point of view of the verification of sum rules. The latter are the power frequency moments of the loss function, a positive even function of frequency directly related to the imaginary part of the inverse dielectric function. The zero moment is shown to coincide with that of the RPA, the f-sum rule is satisfied, and the fourth moment sum rule is verified only partly, without taking the correlations into account. These drawbacks of the Mermin model expression for the dielectric function define the realm of applicability of this approximation.