The energy of the isolated iron nanocluster is calculated by molecular mechanics method using Lennard-Jones potential depending on the position of impurities, i.e., interstitial carbon atom and substitutional nickel atom. The cluster included a carbon atom drifted to the surface from an inner octahedral interstice along the ⟨011⟩ direction or through the tetrahedral interstice firstly in the ⟨1$\bar{1}$1⟩ direction and then in the ⟨111⟩ direction. One of the 14 iron atoms is replaced with a nickel atom in the position, which is changed during simulation. As determined, the positions of a nickel atom significantly affect the energy of the nanocluster. The calculation results in the case of f.c.c. nanocluster indicate that position of a carbon atom at the octahedral interstice is more energy-favourable than its position at the tetrahedral interstice. On the other hand, the potential barrier is smaller in the ⟨1$\bar{1}$1⟩ direction than in the ⟨011⟩ direction. This indicates that two ways for carbon atom drifting to the nanocluster surface are available. The changing of the nickel-atom position significantly influences on the height of the potential barriers of the octahedral and tetrahedral interstitial sites that gives a possibility to manipulate a carbon atom within the near-surface layer of nanocluster. Besides, a carbon atom affects the nanocluster-growth direction, which is estimated by the joining energy for the additional iron atom. The obtained results can be useful in medicine, biology and technologies of nanoelectromechanical systems (NEMS) where both nanoclusters and nanoparticles are used.