[phenixbb] Scattering from riding hydrogens?

[Damian Ekiert]

Hello,

I have a question regarding two parameters and how they affect riding hydrogens.

    contribute_to_f_calc = True
    high_resolution_limit_to_include_scattering_from_h = 1.6

At lower resolution, setting contribute_to_f_calc = false is frequently helpful when using riding hydrogens and has been discussed before.  But what is high_resolution_limit_to_include_scattering_from_h = 1.6 doing?  If scattering from hydrogens is only included at higher than 1.6A resolution, it would seem like contribute_to_f_calc = True/False would not have any effect at say, 3.5A, but comparing identical refinement runs with contribute_to_f_calc = True or contribute_to_f_calc = False clearly gives different results.  Can hydrogens contribute to Fcalc in a way aside from their scattering, or is their contribution accounted for independent of the position of the riding hydrogen (e.g., additional scattering term added to the associated heavy atom)?  I think I am misunderstanding what these two parameters are doing and would appreciate some clarification.  

Thanks,

Damian Ekiert