In any independent particle (IP) model, the motion of individual particles
(e.g. electrons) is not correlated with the motion of other particles,
appart from the Pauli exclusion principle. Interaction between particles
correlate their motions. Thus, one can say that any good IP model
(approximation), describing a well considered system of particles,
includes only the part of the interaction which does not correlate the
motions of the particles. The remaining part of the interaction is called
the residual interaction or the correlation interaction. Conclusion; the
single configuration Dirac-Fock model does NOT include electron
correlation by definition. It can be be proved that all determinental
wave functions formed from a complete set of single particle states make
a complete set of N-particle states. Since each determinental wave
function corresponds to a configuration, this means that all configurations
make a complete set of N-particle states. The actual atomic wave functions
could be developed in the configuration. One can formulate the variational
priciple by using a linear combination of different configurations instead
of a single configuration. In this way, one has a multi-configuration
Hartree-Fock (MCHF) or multi-configuration Dirac-Fock (MCDF) approximation.
This approach includes correlation in the atomic states. Single particle
states are specified with quantum numbers
in the non-relativistic case
or
in the relativistic case.
Some definitions;