Interaction energy between the C
fullerene or Fe@C
endofullerene and (8,8) nanotube. Dependences of the interaction energy E
W between the C20 fullerene (a, b) or Fe@C20 endofullerene (c, d) and the (8,8) nanotube on the fullerene displacement z along the nanotube axis (a, c) and on the angle φ of the fullerene rotation about the nanotube axis (b, d). Solid lines denote nanotube with the Kekule structure, dashed lines denote nanotube with the structure of metallic phase. The energy minimum is positioned at E
W = 0, z = 0 and φ = 0.