Revision of the theory of a uniform electron gas

The many-body theory of a uniform electron gas was developed at the end of 1950ies. The Coulomb interaction between electrons was considered as a perturbation and the ground state energy was calculated in all orders of the non-degenerate perturbation theory. We show that the ground state of the unperturbed system is actually strongly degenerate and that the degenerate perturbation theory leads to lower values of the ground state energy.