Hi Timothy,

the default values (coordinate_sigma = 0.05 , b_factor_weight = 10) should be good in most cases. It depends what you call "looser". Yes, you can make them looser by increasing coordinate_sigma (for refinement of individual coordinates), and decreasing b_factor_weight (for individual isotropic B-factor refinement). You can do it specifically for selected atoms, since you can define as many NCS related groups of atoms as you wish and each defined with their individual weights:

http://phenix-online.org/documentation/refinement.htm#anch24

refinement.ncs.restraint_group {
reference = chain A resid 1:4
selection = chain B and resid 1:3
selection = chain C
coordinate_sigma = 0.05
b_factor_weight = 10
}
refinement.ncs.restraint_group {
reference = chain E
selection = chain F
coordinate_sigma = 0.025
b_factor_weight = 3
}
refinement.ncs.restraint_group {
reference = chain Z and backbone
selection = chain F and backbone
}
refinement.ncs.restraint_group {
reference = chain Z and sidechain
selection = chain F and sidechain
selection = (chain I or chain K) and sidechain
}

Let me know if you have any questions.

Pavel.

On 12/7/10 7:31 PM, Timothy Springer wrote:

Hi, I am using NCS restraints for 4 copies of a molecule at 3.05 Å. We are using the standard weights:

coordinate_sigma = 0.05

b_factor_weight = 10

and the 4 molecules look identical. What are suggested values for looser restraints? One of my colleagues said that varying them did not make a difference- ncs was still very strict. Is there a way to make them less strict?

Thanks,

Timothy A. Springer, Ph.D.