On the application of the symbolic addition procedure in neutron diffraction structure determination

The conditions have been examined for the application of the symbolic addition procedure for the evaluation of signs of structure factors from neutron diffraction data for centrosymmetric crystals containing atoms with both positive and negative scattering factors. It is shown that this procedure can be used directly, without first deriving the squared structure factors, when the contribution of the negative scatterers to the total neutron scattering is less than 25%. Several examples of the use of this method are given. The results show that for E_h ≥ 1.5, the signs of about 95% of the reflexions are determined correctly.