This is a two part question. Also note I am using EXPGUI to interface with GSAS.
1) I am trying to refine a neutron diffraction profile that contains pure Ti at room temperature (HCP structure). I have added a new phase with the P 63 / m m c space group and then added the Ti atom at the 1/3,2/3,1/4 position. The problem I get is that GSAS will not predict the (101) peak which is the major peak. Also of note is that although the Ti atom sits at the 2c site I am getting a multiplicity of 4.
2) Another profile I have has Ni3Ti in it which is also P 63 / m m c. One of the Ni atom positions is at the 1/6, 1/3, 1/4 site. In the international tables an x, 2x, 1/4 has a multiplicity of 6 (6h site) but I am getting a multiplicity of 12
I am wondering what I am doing wrong. Is there some trick with the 194 space group? When I input the space group and check the equivalent positions I am given 12 general positions (the international table gives 24 this would include all generated by lattice centering). When I use Rietan to generate a spectrum it shows the (101) peak. Below are the ouputs of the 12 equivalent positions in Rientan and those of GSAS. I am wondering if anyone could shed some light for me on what is going on. (Note I got the data for GSAS from the spcgroup.exe in the GSAS executable folder. Also I wrote out the GSAS equivalent positions with x's first and the z's before the 1/2 so it was easier to compare to Rietan output)
Rietan
x, y, z
-y, x-y, z
-x+y, -x, z
-x, -y, z+1/2
y, -x+y, z+1/2
x-y, x, z+1/2
y, x, -z
x-y, -y, -z
-x, -x+y, -z
-y, -x+y, -z+1/2
-x+y, y, -z+1/2
x, x-y, -z+1/2
GSAS
x, y, z
x-y, x, z+1/2
-y, x-y, z
-x, -y, z+1/2
-x+y, -x, z
y, -x+y, z+1/2
y, x, z
-x+y, y, z+1/2
-x, -x+y, z
-y, -x, z+1/2
x-y, -y, z
x, x-y, z+1/2
Sorry for the long question. I appreciate any help
It is common to find some bugs in the setting of space groups. Why do not use Rietan, if you think that it rightly functions? You can try to change the occupancy of the site to fix the multiplicity. To halve the multiplicity you can halve the occupancy. I'm not so confident with GSAS but I've found bugs also in commercial softwares. Have you tried FullProf? Is a free program that in general works well
Marcella thank you very much for your response. I guess I was hoping to use GSAS because I am familiar with how it operates and I like the user interface of EXPGUI. But if it seems as though there is a bug in GSAS with this space group then I will need to find an alternate program. I will look into Full Prof and some of the other programs out there.
I tested group 194 with my version of EXPGUI. It gave correct multiplicities and equivalent positions. Could you show a screenshot of the filled 'add new phase' window?
upd: You might have entered P6/3mcm (193) instead of P6/3mmc.
Hi Alexander, I have been meaning to get back here and update this with the answer. I broke down and wrote one of the authors of the program. He very graciously helped me out with my user error so I thank him for that.
My problem lay in how I was inputting the space group. I was putting it in as P 63 / m m c. I left a space between the 63, the / and the m. When I initially imported a cif file into EXPGUI the space group came up with P 63/m m c but EXPGUI gave me a warning saying GSAS may not recognize the space group. So I added the spaces and it was accepted.
In the end it was my user error in putting the spaces in the appropriate place
A FullProf output is attached by generating Wyckoff positions for SG 194.
Thanks Murat. I should clarify that when I input P 63/m m c, EXPGUI provides the correct equivalent positions for the SG 194
Hi All,
is there anyone knows how we can change the bin from even number to odd? for example in the image (attached) below from 2500 to 2501?
I intend to get the local structure following by RMC simulation.
Thanks,
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