We investigate the rms peculiar velocity of galaxy clusters in the Lambda cold dark matter ( \Lambda CDM ) and tau cold dark matter ( \tau CDM ) cosmological models using N-body simulations .
Cluster velocities for different cluster masses and radii are examined .
To identify clusters in the simulations we use two methods : the standard friends-of-friends ( FOF ) method and the method , where the clusters are defined as the maxima of the density field smoothed on the scale R \sim 1 h ^ { -1 } Mpc ( DENSMAX ) .
If we use the DENSMAX method , the size of the selected clusters is similar for all clusters .
We find that the rms velocity of clusters defined with the DENSMAX method is almost independent of the cluster density and similar to the linear theory expectations .
The rms velocity of FOF clusters decreases with the cluster mass and radius .
In the \Lambda CDM model , the rms peculiar velocity of massive clusters with an intercluster separation d _ { cl } = 50 h ^ { -1 } Mpc is \approx 15 % smaller than the rms velocity of the clusters with a separation d _ { cl } = 10 h ^ { -1 } Mpc .