ABINIT Discussion Forums

I am new in crystallography, my major problem now is how to determine xred and kbounds for various systems. Someone can pls explain with this two systems FeO(wustite) and CaB6. Thanks alot in anticipation of your assistance.

Hi!

You have to be more specific. What is the exact problem you're faced with? More details are needed.

Igor L.

Igor,
I dont know how people got those value they put in for xred and kptbounds and i want someone to put through by writing out xred and kptbound for CaB6 and FeO(wustite).

Well, you have to read the variable descriptions first. And then, if you don't understand something or have doubts what you should do in order to do it properly, ask here. You cannot expect someone to do the entire job for you. For crystallography issues, maybe these sites will help you:

http://www.cryst.ehu.es/
http://cst-www.nrl.navy.mil/lattice/

Igor L.

Igol,
Thanks alot, i got to the site http://www.cryst.ehu.es/and kpoints for space group 136 which TiO2 space group are listed as follows,
G 0 0 0
Z 0 0 1/2
M 1/2 1/2 0
A 1/2 1/2 1/2
R 0 1/2 1/2
X 0 1/2 0
Now from ainit example t14.in, kpoints are arrange as follows
kptbounds2 0.5 0.5 0.5 #A
0.0 0.0 0.0 #Gamma
0.5 0.5 0.0 #M
0.5 0.0 0.0 #X
0.0 0.0 0.0 #Gamma
0.0 0.0 0.5 #Z
0.5 0.0 0.5 #R
there is different between the two and i dont know the order i have to follow in arraging my kpoints. Moreover the X points from the website is different from the X in the example. Kindly put me through and bear with me the disturbance am given you. Thanks

If you have a reference with which you could compare your band structure, then it would be the best to follow the same path as in that reference. If not, then you can follow whichever path you like...you should try to make it informative as much as it can be, in order for you to be able to explain your point and/or conclusion.

Because of the symmetries of the tetragonal unit cell you have, there are 2 X points in the Brillouin zone (BZ) with coordinates you saw in the test input file and the other one with the coordinated you saw on the web site. You can see them if you clikc the Brilluoin zone link just above the table on that web site. The one from the test input file is not denoted there, but can be seen as a white point, where k_x axes goes through the BZ side.
For exercise, you can try both X points and see what you will get.

Hope this helps,

Igor L.

Igol L thanks alot, i am getting there gradually. The only problem now is how to get atomic positions coordinates whenever i want to work with high number of atom. See for example, i dont now how someone arrived at this,
# Atomic positions
xred 0.00 0.00 0.00 #Ti1
0.50 0.50 0.50 #Ti2
0.3033485499 0.3033485499 0.00 #O1
-0.3033485499 -0.3033485499 0.00 #O2
0.1966514501 0.8033485499 0.50 #O3
0.8033485499 0.1966514501 0.50 #O4
This person is working on TiO2.
Thanks alot, i count much on you.
-BAMGBOSE, M. K.

You have the positions also on the same web page, just click 'wyckpos' and type the space group number. The exact values of the free parameters are probably calculated using one of the optimization algorithms. Initial values for the optimization are usually taken from references.

Igor L.