  We study electronic structures of two-dimensional quantum dots in strong
magnetic fields using mean-field density-functional theory and exact
diagonalization. Our numerically accurate mean-field solutions show a
reconstruction of the uniform-density electron droplet when the magnetic field
flux quanta enter one by one the dot in stronger fields. These quanta
correspond to repelling vortices forming polygonal clusters inside the dot. We
find similar structures in the exact treatment of the problem using a new type
of operator for the analysis. We discuss important differences and limitations
of the methods used.
