The transformation properties of f(R)YMM(Θ,φ) functions under translation of the reference system along the z axis, apart from those in relation to rotation of the system, have to be known to formulate the effective one-electron crystal field hamiltonian. The classical solution of the problem for a general radial function f(R) in the form of expansion into the spherical harmonic series has been given by Sharma in 1976. Another method avoiding integration but making use of the simple translational behaviour of the multipole functions R−(L + 1)YLM(Θ,Φ), and reduction of the Kronecker products of spherical harmonics, is presented. The method allows one to find the expansion of the f(R)YLM(Θ,Φ) function by means of the 3-j symbols only. The method is applicable to a wide class of radial functions which can be expanded into a power series. Moreover, in the case of crystal field potential, it gives a clear survey of the contributions of each local potential moment to the crystal field parameters.