This is used to randomize the initial model before producing each final model. If set toNonethen no randomization is done, and every model will be the same. You can set it to one of the functions in therandomizemodule —randomize.xyz(the default) to randomize all coordinates of standard residues, orrandomize.dihedralsto randomize dihedral angles. (The amount of randomization carried out by these two functions can be tuned by changingautomodel.deviation.) Finally, you could provide your own Python function; see therandomizemodule inmodlib/modeller/automodel/randomize.pyfor examples to get you started.