Hi xplorers,

I am trying to use different sets of RDCs and was a bit confused by the scaling
function scale_toNH().

I am wondering whether the NH means amide N-HN or nucleic acid N-H group.

In the rdcPotTools.py it says:

scale_toNH(rdc,type=0):
  scales the given expression for dipolar coupling such that given
Da=scale*Da_NHN

But the expression to calculate scale states:

scale = Da_prefactor[type] / Da_prefactor["NH"]

while

Da_prefactor["NH"] = gamma_N * gamma_H / r_nh**3
r_nh = r_caha / (gamma_C/gamma_N*0.48125)**(1./3)

Quite interestingly, given the r_caha, gamma_C, gamma_N values in the
rdcPotTools.py, I get r_nh=0.647731, while r_nhn is 1.042 in the same file.

So if I scale amide N-HN couplings, I do not get a scale factor of 1?

And I also notice 

Da_prefactor["HP"]   = gamma_H * gamma_P
Da_prefactor["HH"]   = gamma_H * gamma_H

Does this mean r_HH, r_HP are set to 1?

And does anyone have the canonical bond distance for Ca & Cb? It would be good
to add type CACB in rdcPotTools.py.
I found the r_?? used to calculate scale factors are different from those in
the protein.par, thus I am not clear which value should I use for scaling.

I am using xplor-nih v2.14

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