  Within investigating the multiple charge spreading generalizing the Bertaut
approach, a set of confined spreading functions with a polynomial behaviour,
but defined so as to enhance the rate of convergence of Coulomb series even
upon a single spreading, is proposed. It is shown that multiple spreading is
ultimately effective especially in the case when the spreading functions of
neighbouring point charges overlap. In the cases of a simple exponential and a
Gaussian spreading functions the effect of multiplicity of spreading on the
rate of convergence is discussed along with an additional optimization of the
spreading parameter in dependence on the cut-off parameters of lattice
summation. All the effects are demonstrated on a simple model NaCl structure.
