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Hello Sonja--
>
> 1) can it be that there is a typing mistake in the nih-sani file:
>
> COEFficient <real> <real> <real>
> {* coef: <DFS> <anisotropy> <rhombicity>
> !a0+a1*(3*cos(theta)^2-1)+a2*(3/2)*sin(theta)^2*cos(2*phi)
> DFS = a0, rhombicity = a2*a1, anisotropy = a1 *}
>
> should the rhombicity not be a2/a1 instead of a2*a1?
well, there are two mistakes:
a2 is actually rhombicity. i.e. the formula should be:
a0+a1*(3*cos(theta)^2-1)+a1*a2*(3/2)*sin(theta)^2*cos(2*phi)
thanks for catching this. I will fix the documentation.
>
> 2) in some of the input files I found negative values for the
> coefficient referred to a a1. I expected a1 to correspond to
> Da (the axial component) of the tensor) and therefore to be
> positive? Or is a1 something else?
While Da is referred to as a magnitude, it can take negative
values. That this is so can be clearly seen from the definition of Da
in pages 133-134 of Bax, Kontaxis and Tjandra, Meth. in Enz. 339 (2001).
best regards--
Charles
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