The excitation spectrum of an electron liquid is represented by a simple, physically motivated model: Spin-symmetric excitations are replaced by a plasmon-pole spectrum, ${\omega }^{\mathrm{pl}\left(\mathrm{q}\right)}$, and spin-antisymmetric excitations are replaced by a paramagnon-pole spectrum, ${\omega }^{\mathrm{pa}\left(\mathrm{q}\right)}$. These frequencies are determined by requiring the model to have the correct density and spin response. Interaction of charged particles with plasmons and paramagnons is found by imposing the f-sum rules. With this model one can easily calculate both charge-induced and spin-induced correlation effects of interacting electrons. In one application we show that the model accounts for the significant narrowing of the occupied conduction band observed in several metals.

• Received 1 August 1985

DOI:https://doi.org/10.1103/PhysRevB.33.925