Formation and stability of the early stage solute and defect clusters in Cu-free ferritic steels during irradiation

•The mechanism of the role of specific element species in the local stability of the Mn-Ni-Si quartet clusters are investigated by DFT.•The interaction of Mn with the dumbbell interstitials is stronger than other solutes. and this is favorable for formation of the cluster.•Si can stabilize solute clusters because it forms stable covalent bonds with other solutes at 1nn.