[MMTK] Question about neutron scattering in nMoldyn

Konrad Hinsen hinsen at cnrs-orleans.fr
Thu Oct 16 18:21:19 UTC 2008

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 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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