Dear Karina,

I think that the answer for sasview 4.2.2 is “local monodisperse”, the same S(Q) is used for all radii in a polydisperse form factor. The default addition of an S(Q) ties the radius used in the S(Q) to the mean radius from the P(Q).  Creating a P(Q)S(Q) product in the “plugin model” editor instead allows a different “effective radius” in the S(Q) to that from the P(Q)

From sasview 4.3 we started to add some further functionality, which is now even further improved in sasview 5 where an option to include the beta(Q) decoupling approximation is introduced. This damps out oscillations due to S(Q) to allow at least approximately for the effects of polydispersity and/or non-spherical particle shapes. Sasview 5 also allows, where appropriate, for different choices of which radius  to use in the S(Q), for example for a cylinder, the half length, the radius or the diagonal radius.

For greater detail I would recommend downloading sasview 5 and reading the improved documentation in that version.

Regards

Richard Heenan

From: users [mailto:users-bounces@lists.sasview.org] On Behalf Of Abitaev, Karina via users
Sent: 07 April 2020 10:04
To: users@sasview.org
Subject: [SasView Users] Sum Multi Function Version 4.2.2

Dear Sasview Team,

I am using Sasview 4.2.2 to fit a colloidal crystal of polymer nanoparticles.
Here I use a Form factor for spheres, where a polydispersity is included. Furthermore, I am using a hard sphere structure factor.

I found the option to multiply the Spheres with hard spheres, so I can supply for each a radius and polydispersity. In this context I was wondering how the structure factor and form factor are combined (decoupling approximation, local monodisperse approx, ...)

Thank you in advance for your help!

Best wishes,

Karina

-- 
Karina Abitaev
Institut für Physikalische Chemie
Universität Stuttgart
Pfaffenwaldring 55
70569 Stuttgart
Germany

karina.abitaev@ipc.uni-stuttgart.de

Phone: +49 (0)711/685-64502
Fax: +49 (0)711/685-64443