We use the Path Integral Monte Carlo method to investigate the interplay
between shell effects and electron correlations in single quantum dots with up
to 12 electrons. By use of an energy estimator based on the hypervirial theorem
of Hirschfelder we study the energy contributions of different interaction
terms in detail. We discuss under which conditions the total spin of the
electrons is given by Hund's rule, and the temperature dependence of the
crystallization effects.Comment: 6 pages, 4 figure