The correlation coefficient between the observed and
calculated structure factors for reflections included in
the refinement.
The correlation coefficient is scale-independent and gives
an idea of the quality of the refined model.
sumi(Foi Fci - <Fo><Fc>)
Rcorr = ------------------------------------------------------------
SQRT{sumi(Foi)2-<Fo>2} SQRT{sumi(Fci)2-<Fc>2}
Fo = observed structure factors
Fc = calculated structure factors
<> denotes average value
summation is over reflections included in the refinement