 The resulting dielectric function, also called the "Lindhard dielectric function", correctly predicts a number of properties of the electron gas, including plasmons.The RPA was criticized in the late 1950s for overcounting the degrees of freedom and the call for justification led to intense work among theoretical physicists.In a seminal paper Murray Gell-Mann and Keith Brueckner showed that the RPA can be derived from a summation of leading-order chain Feynman diagrams in a dense electron gas.