Dear All
We are sorting out Alex's problems off-list but as he is raising many
useful points, I'll post a summary of our fixes later.
Jon has raised an important point that I thought it worth
highlighting- incommensurate structures are not always just P-1.
Magnetic structures are Bloch waves and translate through the crystal
with sine and cosine dependencies. Whether these waves have inversion
symmetry depends on where their origins are...
The space group of a magnetic structure is a whole other discussion!
Cheers
Andrew
On 23 Jul 2009, at 18:19, Jon Wright wrote:
Dear Alexander,
This is theoretically one of the few things that can be done with
PRODD, which is a refinement program based on the CCSL subroutine
library. Some multibank spiral structure refinements were done with
the program when I was doing my thesis.
1) How do I decide on the space group? With incommensurate
structures is it always just P -1
I don't think it is always P-1. With CCSL you either have symmetry
elements as part of the magnetic symmetry, or not, called MSYM or
NSYM. It was rather difficult to figure out.
5) Atom types: Where in the manual do I find the correct types I
have to use? Is it always just M in front of the atom?
With CCSL you look up the magnetic form factors and put them in the
input file with whatever names you like :-)
Sorry I can't help much on the fullprof questions. Since you seem to
have a multi-k structure, for PRODD you would need at least two
phases to do that. I remember spending some time trying with
fullprof but eventually learned a valuable lesson about why source
code is useful. If you like, I'd be happy to send you the PRODD
sources and try to dig out some examples. Even better, you could
tidy the sources up and merge them with the current CCSL,
realistically I am never going to find the time to do it myself.
Spiral magnetic structures are a fantastic way to learn about
crystallography and reciprocal space. Good luck!
Jon
