Item _refine.overall_SU_ML

Description

              The overall standard uncertainty (e.s.d.) of the positional
               parameters based on a maximum likelihood residual.

               The overall standard uncertainty (sigma~X~)^2 gives an
               idea of the uncertainty in the position of averagely
               defined atoms (atoms with B values equal to average B value)

                    3                         N_a
    (sigma~X~)^2  = -----------------------------------------------------
                    8 pi^2 sum~i~ {(1/Sigma - (E_o)^2 (1-m^2)(SUM_AS)s^2}

               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        =  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              = is form factor of atoms
               delta_x        = expected error
               m              = is figure of merit of phases of reflection
                                included in summation delta_x expected error
               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) "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/

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