International
Tables for
Crystallography
Volume F
Crystallography of biological macromolecules
Edited by M. G. Rossmann and E. Arnold

International Tables for Crystallography (2006). Vol. F, ch. 25.2, p. 713   | 1 | 2 |

Figure 25.2.3.4 

A. T. Brunger,v* P. D. Adams,e W. L. DeLano,f P. Gros,g R. W. Grosse-Kunstleve,e J.-S. Jiang,h N. S. Pannu,i R. J. Read,j L. M. Ricek and T. Simonsonl
[Figure 25.2.3.4]
Figure 25.2.3.4

Examples of symbolic definition of a refinement target function and its derivatives with respect to the calculated structure-factor arrays. (a) Simultaneous refinement of heavy-atom sites of three derivatives. The target function is defined by the `target' expression. `[\hbox{f}\_\hbox{h}\_1]', `[\hbox{f}\_\hbox{h}\_2]' and `[\hbox{f}\_\hbox{h}\_3]' (in bold) are complex structure factors corresponding to three sets of heavy atoms that are specified using atom selections [equation (25.2.3.7)[link]]. The target function and its derivatives with respect to the three structure-factor arrays are defined symbolically using the structure-factor amplitudes of the native crystal, `[\hbox{f}\_\hbox{p}]', those of the derivatives, `[\hbox{f}\_\hbox{ph}\_1]', `[\hbox{f}\_\hbox{ph}\_2]', `[\hbox{f}\_\hbox{ph}\_3]', the complex structure factors of the heavy-atom models, `[\hbox{f}\_\hbox{h}\_1]', `[\hbox{f}\_\hbox{h}\_2]', `[\hbox{f}\_\hbox{h}\_3]', and the corresponding lack-of-closure variances, `[\hbox{v}\_1]', `[\hbox{v}\_2]' and `[\hbox{v}\_3]'. The summation over the selected stucture factors (`tselection') is performed implicitly. (b) Refinement of two independent models against perfectly twinned data. `fcalc1' and `fcalc2' are complex structure factors for the models that are related by a twinning operation (in bold). The target function and its derivatives with respect to the two structure-factor arrays are explicitly defined.