[MMTK] Question about neutron scattering in nMoldyn

Ramon Crehuet rcrehuet at gmail.com
Fri Oct 17 07:38:13 UTC 2008


Thanks a lot!
This information helps, but raises new questions...
1) Given that experimental results do not state the angular resolution of
the apparatus, is the default value in nmoldyn a reasonable choice? (for
more details, we are trying to compare with results obtained in the IN13 at
the ILL)
2) How can the energy resolution be introduced? Jeremy Smith has a
interesting paper (Biophys. J, 82, p. 1216) showing that this parameter
influences the measured <u^2>. And he does it with nmoldyn!
Thanks again for your attention,
Ramon



2008/10/16 Konrad Hinsen <hinsen at cnrs-orleans.fr>

> On 16.10.2008, at 18:48, Ramon Crehuet wrote:
>
>  trajectory in the low q-range. Apart from the q values, you have to
>> specify the "Q shell width". In the manual is is said that it fixes the
>> q-resolution, but I do not understand the meaning. Is this parameter
>> related to the energy resolution of the neutron spectrometer? If so,
>> which is this relationship?
>>
>
> Every structure factor value is calculated as an orientational average over
> q-vectors with the same length - or rather almost the same length. In
> practice, the average is calculated over q vectors from a spherical shell
> whose mean radius is given by the q value and whose thickness is given by "Q
> shell width".
>
> The Q width parameter exists mostly for computational reasons: in a
> periodic system, except for very high Q values, it is not feasible to pick Q
> vectors of exactly the same length because there are not enough of them. But
> it can also be identified with the angular (not the energetic) resolution of
> the neutron spectrometer.
>
> Hope this helps,
>  Konrad.
> --
> ---------------------------------------------------------------------
> Konrad Hinsen
> Centre de Biophysique Moléculaire, CNRS Orléans
> Synchrotron Soleil - Division Expériences
> Saint Aubin - BP 48
> 91192 Gif sur Yvette Cedex, France
> Tel. +33-1 69 35 97 15
> E-Mail: hinsen at cnrs-orleans.fr
> ---------------------------------------------------------------------
>
>
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