  A simple model for the dielectric function of a completely ionized plasma
with an arbitrary ionic charge, that is valid for long-wavelength
high-frequency perturbations is derived using an approximate solution of a
linearized Fokker-Planck kinetic equation for electrons with a Landau collision
integral. The model accounts for both the electron-ion collisions and the
collisions of the subthermal (cold) electrons with thermal ones. The relative
contribution of the latter collisions to the dielectric function is treated
phenomenologically, introducing some parameter $\varkappa$ that is chosen in
such a way as to get a well-known expression for stationary electric
conductivity in the low-frequency region and fulfill the requirement of a
vanishing contribution of electron-electron collisions in the high-frequency
region. This procedure ensures the applicability of our model in a wide range
of plasma parameters as well as the frequency of the electromagnetic radiation.
Unlike the interpolation formula proposed earlier by Brantov et al. [Brantov et
al., JETP 106, 983 (2008)], our model fulfills the Kramers-Kronig relations and
permits a generalization for the cases of degenerate and strongly coupled
plasmas. With this in mind, a generalization of the well-known Lee-More model
[Y. T. Lee and R. M. More, Phys. Fluids 27, 1273 (1984)] for stationary
conductivity and its extension to dynamical conductivity [O. F. Kostenko and N.
E. Andreev, GSI Annual Report No. GSI-2008-2, 2008 (unpublished), p. 44] is
proposed for the case of plasmas with arbitrary ionic charge.
