 Kohn anomalies arise together with Friedel oscillations when one considers the Lindhard approximation instead of the Thomas–Fermi approximation in order to find an expression for the dielectric function of a homogeneous electron gas.The expression for the real part formula_2 of the reciprocal space dielectric function obtained following the Lindhard theory includes a logarithmic term that is singular at formula_3, where formula_4 is the Fermi wavevector.Although this singularity is quite small in reciprocal space, if one takes the Fourier transform and passes into real space, the Gibbs phenomenon causes a strong oscillation of formula_5 in the proximity of the singularity mentioned above.