  The possibility to use perturbation theory to systematically improve
calculations on circular quantum dots is investigated. A few different starting
points, including Hartree-Fock, are tested and the importance of correla- tion
is discussed. Quantum dots with up to 12 electrons are treated and the effects
of an external magnetic field are examined. The sums over excited states are
carried out with a complete finite radial basis set obtained through the use of
B splines. The calculated addition energy spectra are compared with experiments
and the implications for the filling sequence of the third shell are discussed
in detail.
