Index

Macromolecular dictionary (mmCIF) version 2.0.09

_refine.overall_SU_B

Definition:

   The overall standard uncertainty (estimated standard deviation)
   of the displacement parameters based on a maximum-likelihood
   residual.

   The overall standard uncertainty (sigma~B~)^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).

                                 N_a
    (sigma~B~)^2  = 8 ----------------------------------------------
          sum~i~ {[1/Sigma - (E_o)^2 (1-m^2)](SUM_AS)s^4}

   SUM_AS         = (sigma_A)^2/Sigma^2
   N_a            = number of atoms
   Sigma          = (sigma_{E;exp})^2 + epsilon [1-(sigma_A)^2]
   E_o            = normalized structure factors
   sigma_{E;exp}  = experimental uncertainties of normalized
                    structure factors
   sigma_A        = <cos 2 pi s delta_x> SQRT(Sigma_P/Sigma_N)
                    estimated using maximum likelihood
   Sigma_P        = sum_{atoms in model} f^2
   Sigma_N        = sum_{atoms in crystal} f^2
   f              = form factor of atoms
   delta_x        = expected error
   m              = figure of merit of phases of reflections
                    included in the summation
   s              = reciprocal-space vector
   epsilon        = multiplicity of diffracting plane

   summation is over all reflections included in refinement

   Ref: (sigma_A 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 ML 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

Type: float

Mandatory item: no

Category: refine