The xrefin optimize overall statement optimizes overall isotropic or anisotropic B-factors by employing a conjugate gradient minimization using (Eq. 12.1) as the target. For the isotropic case, the variable is simply the overall B-factor B, and in Eq. 12.1 is replaced by
For the anisotropic case, the variables are the six parameters of the anisotropic B-factor tensor , and in Eq. 12.1 is replaced by
Normally, the following restrictions apply to the anisotropic B-factor tensor (see RESTriction statement):
the program modifies the structure factors and the
B atomic property array (Section 2.16).
In the isotropic case,
it adds the refined B-factor shift to the B array and it also applies
the B-factor shift to the structure factors.
In the anisotropic case,
the overall isotropic contribution is subtracted from the tensor such that the trace of B is zero. This modified B tensor is then applied to the calculated structure factors. The overall isotropic contribution is added to the B-factor array .
Note that is not touched during this procedure.