CORRELATIONS AND LOCAL-DENSITY APPROXIMATION

We compute the RPA correlations explicitly for small, closed shell Na clusters up to Na92 and compare it with the correlations described by energy-density functionals in the local-density approximation. We find an excellent agreement of the correlation energies between explicit calculation and local-density approximation. The correlations on the density distribution, or the corresponding form factor, agree fairly well for the gross properties but fail badly for detailed structures at small wavelengths.