  We present a dynamic model to study ordering of particles on arbitrary curved
surfaces. Thereby the particles are represented as maxima in a density field
and a surface partial differential equation for the density field is solved to
the minimal energy configuration. We study annihilation of dislocations within
the ordered sytem and premelting along grain boundary scars. The obtained
minimal energy configurations on a sphere are compared with existing results
and scaling laws are computed for the number of excess dislocations as a
function of system size.
