The overall standard uncertainty (estimated standard deviation)
of the displacement parameters based on a maximum-likelihood
residual.
The overall standard uncertainty (sigmaB)2 gives an idea
of the uncertainty in the B values of averagely defined
atoms (atoms with B values equal to the average B value).
Na
(sigmaB)2 = 8 ----------------------------------------------
sumi {[1/Sigma - (Eo)2 (1-m2)](SUM_AS)s4}
Na = number of atoms
Eo = normalized structure factors
m = figure of merit of phases of reflections
included in the summation
s = reciprocal-space vector
SUM_AS = (sigmaA)2/Sigma2
Sigma = (sigma{E;exp})2 + epsilon [1-(sigmaA)2]
sigma{E;exp} = experimental uncertainties of normalized
structure factors
sigmaA = <cos 2 pi s deltax> SQRT(SigmaP/SigmaN)
estimated using maximum likelihood
SigmaP = sum{atoms in model} f2
SigmaN = sum{atoms in crystal} f2
f = atom form factor
deltax = expected error
epsilon = multiplicity of diffracting plane
summation is over all reflections included in refinement
Ref: (sigmaA estimation) "Refinement of macromolecular
structures by the maximum-likelihood method",
Murshudov, G. N., Vagin, A. A. & Dodson, E. J. (1997).
Acta Cryst. D53, 240-255.
(SU B estimation) Murshudov, G. N. & Dodson,
E. J. (1997). Simplified error estimation a la
Cruickshank in macromolecular crystallography.
CCP4 Newsletter on Protein Crystallography, No. 33,
January 1997, pp. 31-39.
http://www.ccp4.ac.uk/newsletters/newsletter33/murshudov.html