  The low-lying eigenstates of a system of two electrons confined within a
two-dimensional quantum dot with a hard polygonal boundary are obtained by
means of exact diagonalization. The transition from a weakly correlated charge
distribution for small dots to a strongly correlated "Wigner molecule" for
large dots is studied, and the behaviour at the crossover is determined. In
sufficiently large dots, a recently proposed mapping to an effective
charge-spin model is investigated, and is found to produce the correct ordering
of the energy levels and to give a good first approximation to the size of the
level spacings. We conclude that this approach is a valuable method to obtain
the low energy spectrum of few-electron quantum dots.
