/// The coefficients from Waasmaier & Kirfel (1995), Acta Cryst. A51, 416-431.
///
/// @param charge The charge for which the structure values should be returned, use @ref kWSKFVal to return the Cval and Siva values
/// @param charge The charge for which the structure values should be returned, use @ref cif::atom_type_traits::kWSKFVal to return the Cval and Siva values
/// @return The scattering factors as a @ref SFData struct