Let us consider relativistic particle (electron) which moves with relativistic speed $v$ in the Coulomb field (in the field of a fixed heavy nucleus). The main question is what is the potential energy of a particle in such a static field? Landau and Lifshitz in their book "Field Theory" believe that the potential energy is not renormalized in any way and is equal to $\frac{qQ}{r}$. At the same time, a number of authors of original articles on this topic introduce a reduced distance $r\sqrt{1-v^2/c^2}$ into the denominator of this fraction due to the relativistic effect of the reduction in linear dimensions. Which of them is right?