Average figure of merit of phases of reflections not included
in the refinement.
This value is derived from the likelihood function.
FOM = I1(X)/I0(X)
I0, I1 = zero- and first-order modified Bessel functions
of the first kind
X = sigmaA |Eo| |Ec|/SIGMA
Eo, Ec = normalized observed and calculated 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 = form factor of atoms
deltax = expected error
SIGMA = (sigma{E;exp})2 + epsilon [1-(sigmaA)2]
sigma{E;exp} = uncertainties of normalized observed
structure factors
epsilon = multiplicity of the diffracting plane
Ref: Murshudov, G. N., Vagin, A. A. & Dodson, E. J. (1997).
Acta Cryst. D53, 240-255.