  Using variational quantum Monte Carlo method, the effect of Landau-level
mixing on the lowest-energy--state diagram of small quantum dots is studied in
the magnetic field range where the density of magnetic flux quanta just exceeds
the density of electrons. An accurate analytical many-body wave function is
constructed for various angular momentum and spin states in the lowest Landau
level, and Landau-level mixing is then introduced using a Jastrow factor. The
effect of higher Landau levels is shown to be significant; the transition lines
are shifted considerably towards higher values of magnetic field and certain
lowest-energy states vanish altogether.
