Comment on "Theory of electron energy loss in a random system of   spheres"
  In a recent paper, Barrera and Fuchs [Phys. Rev. B 52, 3256 (1995)] provide a theory of electron energy loss in a random system of spheres. In this comment, we point out that the approach of Barrera and Fuchs (A) completely ignores magnetic excitations and retardation, which is inconsistent with the data of energy loss of fast electrons, (B) does not yield the correct k-->0 limit, hence, does not recover correctly the Maxwell-Garnett formula, and (C) does not use the correct screened potential at any k. 
Liang Fu and Lorenzo Resca (Department of Physics, the Catholic   University of America, Washington D.C.)