Collective interactions in a quantum well: The inclusion of nonlocal exchange

We present a variational scheme for calculating the irreducible polarizability of an electron system and apply this method to the exchange interaction in a single quantum well. The collective spin-density and intersubband plasmon energies are derived and evaluated numerically in an infinite-square-well approximation. These results are compared with experiments as well as with the previous theoretical results based upon the local-density approximation.