The density fitting procedure in adf is carried out separately for each pair of atoms. The implemented approach has several advantages in efficiency but it has a drawback in that it necessitates the use of all available fit functions rather than only the symmetric combinations although the final result of course needs only a symmetric fit because the total density is a symmetric (A1) function. For atoms far apart the density fitting is performed with only symmetric functions. Given the implemented algorithm this entails an approximation which can be tuned:
A1FIT atomicseparation
atomicseparation
is the threshold distance between atoms, in Angstrom. The symmetric fit approximation is applied only for atoms farther apart. Default is 10.0 Angstrom
