The overall standard uncertainty (e.s.d.) of the thermal
parameters based on the free R value.
The overall standard uncertainty gives an idea of the
uncertainty in the B values of averagely defined atoms
(atoms with B values equal to the average B value).
N_a
(sigma_B)2 = 0.65 ----- (R_free)2 (D_min)2 C(-2/3)
N_o
N_a = number of atoms
N_o = number of reflections included in refinement
N_p = number of refined parameters
R_free = conventional free crystallographic R-value calculated
using reflections not included in refinement
D_min = maximum resolution
C = completeness of data
Ref: Cruickshank, D. W. (1997). "Refinement of macromolecular
structures". Proc. CCP4 study weekend.
"Simplified error estimation a la Cruickshank in
macromolecular crystallography", Murshudov G. N. &
Dodson E. J. (1997). CCP4 Newsletter, no. 33.
http://www.dl.ac.uk/CCP/CCP4/newsletter33/