Individual B-Factor Refinement

This statement optimizes individual (restrained) isotropic B-factors. Distinctions between backbone and side-chain B-factor restraints can be made by appropriate selections. B-factors of atoms are both selected in xrefin and free to move. The procedure minimizes the target function
\end{displaymath} (14.3)

where the restraining term $E_R$ is given by
$\displaystyle E_R$ $\textstyle =$ $\displaystyle W_B \sum_{(i,j)-bonds} (B_i-B_j)^2/{\sigma_{bonds}}^2$ (14.4)
    $\displaystyle + W_B \sum_{(i,j,k)-angles} (B_i-B_k)^2/{\sigma_{angles}}^2$  
    $\displaystyle + W_B \sum_{k-group} \sum_{j-equivalences}
\sum_{i-unique \; atoms}
(B_{ijk} - \bar{B}_{ik})^2/{\sigma_{ncs}}^2$  

The summations are carried out over all bond and angle terms present in the molecular structure that involve selected and free atoms. The last sum is used only if non-crystallographic symmetry restraints are present (see Chapter 18). The Powell conjugate gradient minimization method is used.


Xplor-NIH 2024-06-11