  We have computed optical Zeeman spectra of magnetic white dwarfs for field
strengths between 10 and 200MG and effective temperatures between 8000 and
40000K. They form a database containing 20628 sets of flux and circular
polarization spectra. A least-squares optimization code based on an
evolutionary strategy can recover relatively complex magnetic field topologies
from phase-resolved synthetic Zeeman spectra of rotating magnetic white dwarfs.
We consider dipole and quadrupole components which are non-aligned and shifted
off-centre. The model geometries include stars with a single high-field spot
and with two spots separated by approx. 90 degrees. The accuracy of the
recovered field structure increases with the signal-to-noise ratio of the input
spectra and is significantly improved if circular polarization spectra are
included in addition to flux spectra. We discuss the strategies proposed so far
to unravel the field geometries of magnetic white dwarfs.
