In the Lorentz–Vlasov model of a plasma the ions are assumed to be fixed in space with disordered distribution, and the Coulomb interaction between electrons is approximated by the Vlasov field, calculated self-consistently from the electron position–momentum distribution function. If correlations between ions are neglected, then the dynamical conductivity of the plasma may be evaluated from the dynamics of the electron gas in interaction with a single ion, the remaining ions being approximated by a uniform background. In dielectric or energy-loss theory, the dynamical friction coefficient is expressed in terms of the dielectric function of the uniform electron gas. A more detailed theory must take full account of the scattering of electrons by the selected ion. It is shown for an electron gas at zero temperature and metallic density, and for a simple ion pseudopotential, that the frequency dependence of the friction coefficient differs appreciably from that predicted by energy-loss theory.