  A comprehensive first principles study on the electronic topological
transition in a number of 122 family of Fe based superconductors is presented.
Doping as well as temperature driven Lifshitz transitions are found from first
principles simulations in a variety of Fe based superconductors that are
consistent with experimental findings. In all the studied compounds the
Lifshitz transitions are consistently found to occur at a doping concentration
where superconductivity is highest and magnetism disappears. Systematically,
the Lifshitz transition occurs in the electron Fermi surfaces for hole doping,
whereas in hole Fermi surfaces for electron doping as well as iso-electronic
doping. Temperature driven Lifshitz transition is found to occur in the
iso-electronic Ru-doped BaFe$_2$As$_2$ compounds. Fermi surface areas are found
to carry sensitivity of topological modifications more acutely than the band
structures and can be used as a better experimental probe to identify
electronic topological transition.
