In the framework of the Thomas-Fermi theory, we arrive at a similar result, yet the proportionality constant κ does not depend on temperature. The main core assumption here is the local linear proportionality between the screening potential V (r) and the screening charge ϱ(r), valid only for the localized electrons rather than the nearly free ones. However, Friedel showed (using his famous sum rule) that instead of the exponential decay, we obtain the oscillatory power decay, Friedel oscillations, of the form ϱ(r) ≈ cos(2kF r + δ)/r 3 .