# 4.23. *FC*: Calculated structure factors

**Authors:** Syd Hall, Jim Stewart, Richard Alden & Jim Holden

**Contact:** Syd Hall,Crystallography Centre,
University of Western Australia, Nedlands 6907, Australia

*FC calculates structure factors when refinement of atomic parameters is not
required.*

## 4.23.1. Calculation Performed

The asymmetric set of atomic sites is entered from the input archive bdf, and
is used to generate symmetrically related sites for all atoms in the unit cell.
The structure factor calculation is applied to these sites. The coordinates of
all sites in a cell may be listed by entering the line "`reset psta 4`"
prior to the FC line.

Overall isotropic, individual isotropic, individual anisotropic, or mixed
individual thermal displacement parameters may be applied in FC. Dispersion
factors and isotropic extinction corrections may also be applied provided
prerequisite data is present on the input bdf.

If requested FC will calculate, and store on the bdf, the Sim (1960) weight.

w(Sim) = I_{1}(*f*) / I_{0}(*f*)
where *f* = 2 F_{o}F_{c}/ f^{2}

## 4.23.3. Example

In this example, structure factors are calculated using all atoms in the bdf.
Dispersion corrections will be applied. All reflections for which F(rel) and
F(cal) differ by more than 7.5 will be listed. In addition, for this
calculation, the F relative scale factor is to be set to 1.013 for scale group
1. When the updated bdf is written it will include F(cal), the estimated phase
and the contributions to A and B from dispersion.

## 4.23.4. References

Henry, Norman and Lonsdale, Kathleen, 1965. Eds. *International Tables for
X-Ray Crystallography Vol. I. *Birmingham, England: Kynoch Press.

Sim, G.A. (1960)* Acta Cryst*. **13**, 511.