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

$$T=E_{XREF}+E_{R}$$ (14.3)

where the restraining term $E_R$ is given by

$$E_R = W_B \sum_{(i,j)-bonds} (B_i-B_j)^2/{\sigma_{bonds}}^2$$ (14.4)

$$+ W_B \sum_{(i,j,k)-angles} (B_i-B_k)^2/{\sigma_{angles}}^2$$

$$+ W_B \sum_{k-group} \sum_{j-equivalences} \sum_{i-unique \; atoms} (B_{ijk} - \bar{B}_{ik})^2/{\sigma_{ncs}}^2$$

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.