  The formation process, properties, and spatial distribution of galaxy groups
and clusters are closely related to the background cosmological model. We use
numerical simulations of variants of the CDM model with different cosmological
parameters in order to compare statistical measures such as mass spectra,
merging histories, correlation functions, and clustering power spectra with
relevant observations. The study of the time evolution shows that the internal
structure of galaxy groups and clusters is connected with their merging
history. Here we discuss the virialisation and the halo's spin parameters.
