samm
Hello,
I am a new user trying a Rietveld refinement of a zeolite (Formula SiO2) which has 85 unique atoms in the cell, I would like to apply soft restraints globally to all SiO4 tetrahedra and Si-(O)-Si distances (O-Si-O=109.5Deg,Si-O =1.62Ang and Si-Si=3.1Ang).
I tried using
AI_Anti_bump(Si*, O*, 1.62, 1)
AI_Anti_bump(Si*, Si*, 3.1, 1)
It just blows up as I kind of expected, it looks like it is taking all Si-Si distances and trying to make them 3.08, whereas I just want those bonded through an oxygen to be taken into account. Is there a way to define a region, say all Si-Si distance from 2.9-3.3 to stay within that range and try and get to 3.1?
Really I'm looking for a way to do this without typing in all the individual bond lengths and bond angles that i want to restrain using 'Distance_Restrain', due to the large number of atoms in the cell and how many other zeolites I need to process in this way.
Is there anybody who would be willing to share a topas.inp file of a zeolite they have done with restraints for me to have a look at and use as a guide?
Many thanks, Sam
johnsoevans
Sam,
I think setting up the distance and angles restraints properly is the only way forward. You can get a list of the relevant distances and angles using "append_bond_lengths" so it's just a case of reformatting that output. Your other option (which might be better if the structure is complex and you only have powder data) is to use rigid bodies for tetrahedra.
John