Signal modelling systematics at ATLAS

For the analysis of various properties of the top quark, parameters like selection efficiency are taken from simulated event samples. These samples need several input parameters, like the top quark mass, the strength of initial and final state radiation or parton distribution functions. The presented results will depend on the choice of these input parameters. Therefore it is mandatory to determine a range of parameters which is consistent with current measurements and is able to determine the systematic uncertainty on the measurement result due to the input of certain parameters in the signal generation. In these proceedings the procedures used by the ATLAS experiment at the LHC are given.