One-and-a-half wavelength approach

Dauter, Z.

doi:10.1107/S0907444902016645

Figure 2
The structure factor of a reflection with its anomalous scattering contribution. In this and all subsequent figures, the contribution of normally scattering atoms is represented by black vectors, the normal scattering of anomalous scatterers by red vectors, the anomalous scattering (real and imaginary contributions) by brown vectors and the total structure factor by blue vectors. (a) The contributions of N normally scattering atoms add up and can be represented by the vector F_N = $[\textstyle \sum_{i}^{N}f^{0}_{i}]$ exp 2πi(h·r_i). The A anomalous scatterers contribute individually to the total normal diffraction F_A = $[\textstyle \sum_{j}^{A}f'_{i}]$ exp[2πi(h·r_j)], the real part of the anomalous correction $[F'_{A}]$ = $[\textstyle \sum^{A}_{j}f'_{j}]$ exp[2πi(h·r_j)] and the imaginary part of the anomalous correction $[F''_{A}]$ = $[\textstyle \sum^{A}_{j}f''_{j}]$ exp[2πi(h·r_j)]. If all anomalous scatterers are of the same kind, vector $[F''_{A}]$ preceeds F_A by 90°. (b) The vector diagram for the Friedel pair, F(h) and F(−h). In relation to F(h), all vectors representing the real contributions to the structure factor have negated phases, whereas the imaginary component $[F''_{h}]$ has its phase shifted by 90° forward from F_A. (c) It is customary to reflect the vectors of the negative Friedel mate, F(−h), across the horizontal axis and represent it as a complex conjugate, ^*F(−h), which more clearly illustrates the relations between vectors and phases of the Friedel mates.

BIOLOGICAL
CRYSTALLOGRAPHY

ISSN: 1399-0047

Volume 58| Part 11| October 2002| Pages 1958-1967

doi:10.1107/S0907444902016645

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