Error refining large number of atoms

lavn2

I have a unit cell containing some organic molecules. Consequently the number of atomic sites is very large (~58). When I attempt a refinement with all the sites positions, I get the following error:

*** Error loading sstring_in at
    { @ }
     unknown or misplaced keyword.
    at LINE 71
    See log file C:\TOPAS5\topas.log

However there are no mistakes in the code - i.e. my placement of @ symbols is fine. There are just a very large number of parameters being refined.

I have tried adding the constraints from the relevant tutorial [1] but this doesn't change anything. My questions are:

(1) is there a constraint on the number of sites allowable in a unit cell - and have I exceeded it?
(2) is there a constraint on the number of parameters that can be refined? for x, y, and z, and for 58 atoms, that is a large number of parameters.
(3) does anyone have a suggestion for how to approach this problem?

Thanks,
Liam

[1] https://community.dur.ac.uk/john.evans/topas_workshop/tutorial_organicriet.htm

johnsoevans

There’s no limit on the number of sites. I’ve used strs with 1000’s of sites succesfully. My guess is you have an error in the INP file. It’s common for the error to be earlier than indicated. It might be that line 71 is the first place where topas reaches an instruction that couldn’t possibly be correct.

lavn2

Hi John

You were right. For one of the atoms (not the one on line 71) the @ symbol refining the z parameter was placed before the "z" not after it.

Thanks for your help.

Liam