Correlation coefficient of electron density for each residue or ligand,
side chain, main chain
The density correlation coefficient is calculated for each component
from atomic densities of (2Fobs-Fcalc) map - "Robs" and the model
map (Fcalc) - "Rcalc" :
D_corr = <Robs><Rcalc>/sqrt(<Robs**2><Rcalc**2>)
where <Robs> is the mean of "observed" densities of atoms of the
component (backbone or side chain).
<Rcalc> is the mean of "calculated" densities of
The value of density for some atom from map R(x) is:
sum_i ( R(xi) * Ratom(xi - xa) )
Dens = ----------------------------------
sum_i ( Ratom(xi - xa) )
where Ratom(x) is atomic electron density for the x-th grid point.
xa - vector of the centre of atom.
xi - vector of the i-th point of grid.
Sum is taken over all grid points which have distance
from the center of the atom less than the Radius_limit.
For all atoms Radius_limit = 2.5 A.
Ref: Vaguine, A.A., Richelle, J. & Wodak, S.J. (1999). Acta Cryst. D55,199-205