              The a3 Cromer-Mann scattering-factor coefficient used to\
               calculate the scattering factors for this atom type.\
\
               Ref: International Tables for X-ray Crystallography, Vol. IV,\
                    (1974). Table 2.2B.\
                or: International Tables for Crystallography, Vol. C,\
                    (1991). Tables 6.1.1.4 and 6.1.1.5.