International
Tables for
Crystallography
Volume B
Reciprocal space
Edited by U. Shmueli

International Tables for Crystallography (2006). Vol. B, ch. 1.2, pp. 23-24   | 1 | 2 |

Section 1.2.13. The generalized structure factor

P. Coppensa*

aDepartment of Chemistry, Natural Sciences & Mathematics Complex, State University of New York at Buffalo, Buffalo, New York 14260-3000, USA
Correspondence e-mail: coppens@acsu.buffalo.edu

1.2.13. The generalized structure factor

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In the generalized structure-factor formalism developed by Dawson (1975)[link], the complex nature of both the atomic scattering factor and the generalized temperature factor are taken into account. We write for the atomic scattering factor: [\eqalignno{f_{j} ({\bf H}) &= f_{j, \, c} ({\bf H}) + if_{j, \, a} ({\bf H}) + f^{'}_{j} + if^{''}_{j} &(1.2.13.1a)\cr T_{j} ({\bf H}) &= T_{j, \, c} ({\bf H}) + iT_{j, \, a} ({\bf H}) &(1.2.13.1b)}] and [F({\bf H}) = A({\bf H}) + iB({\bf H}), \eqno(1.2.13.2)] where the subscripts c and a refer to the centrosymmetric and acentric components, respectively. Substitution in (1.2.4.2)[link] [link] [link] [link] gives for the real and imaginary components A and B of [F({\bf H})] [\eqalignno{A ({\bf H}) &= {\textstyle\sum\limits_{j}} (f_{j, \, c} + f^{'}_{j}) [\cos (2\pi {\bf H} \cdot {\bf r}_{j}) T_{c} - \sin (2\pi {\bf H} \cdot {\bf r}_{j}) T_{a}]\cr &\quad - (f_{j, \, a} + f^{''}_{j}) [\cos (2\pi {\bf H} \cdot {\bf r}_{j}) T_{a} + \sin (2\pi {\bf H} \cdot {\bf r}_{j}) T_{c}]\cr&&(1.2.13.3a)}] and [\eqalignno{B ({\bf H}) &= {\textstyle\sum\limits_{j}} (f_{j, \, c} + f^{'}_{j}) [\cos (2\pi {\bf H} \cdot {\bf r}_{j}) T_{a} + \sin (2\pi {\bf H} \cdot {\bf r}_{j}) T_{c}]\cr &\quad + (f_{j, \, a} + f^{''}_{j}) [\cos (2\pi {\bf H} \cdot {\bf r}_{j}) T_{c} - \sin (2\pi {\bf H} \cdot {\bf r}_{j}) T_{a}]\cr& &(1.2.13.3b)}] (McIntyre et al., 1980[link]; Dawson, 1967[link]).

Expressions (1.2.13.3)[link] [link] illustrate the relation between valence-density anisotropy and anisotropy of thermal motion.

References

Dawson, B. (1967). A general structure factor formalism for interpreting accurate X-ray and neutron diffraction data. Proc. R. Soc. London Ser. A, 248, 235–288.
Dawson, B. (1975). Studies of atomic charge density by X-ray and neutron diffraction – a perspective. In Advances in structure research by diffraction methods. Vol. 6, edited by W. Hoppe & R. Mason. Oxford: Pergamon Press.
McIntyre, G. J., Moss, G. & Barnea, Z. (1980). Anharmonic temperature factors of zinc selenide determined by X-ray diffraction from an extended-face crystal. Acta Cryst. A36, 482–490.








































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