³In the expression for calculating Δp_i, i - i_ref may be replaced by ∕Δi, where Δi is a free parameter for controlling the sharpness of the transition between the two domains in momentum space. However, Δi = 1 provides the adequate number of point, of the order of 5, in order to avoid both a large jump, or a too smooth transition that may lead to violation of the condition that δ < 1 for small i values.