On 29/09/17 09:28, Omamuyovwi Akemu wrote:
Dear QE users,
I apologize if the question seem trivial. I have searched the pw-forum
archive for a solution but did not get any.
I want to set up the input of a BCC material using ibrav= 0
When I set ibrav=3, the structure looks okay from xcrysden
What do you mean by "ok"? Does it look like a cube with many atoms in
it, or like the actual unit cell of the BCC lattice ?
Try pressing F3 and F4 to switch between the conventional cubic cell and
he actually BCC unit cell. Does this solve your problem?
I've attached two images of BCC Iron, for exactly the same input, one is
the conventional cell, the other is the BCC cell. Note that the
conventional cell has twice as many atoms, i.e. it is a supercell
&SYSTEM
ibrav = 3,
celldm(1) = 6.475745143,
nat = 1,
ntyp = 1,
But with ibav=0 and the CELL_PARAMETER card included, the structure
looks different (not BCC).
&SYSTEM
ibrav = 0,
celldm(1) = 6.475745143,
nat = 1,
ntyp = 1,
.....
CELL_PARAMETERS
0.500000 0.500000 0.500000
-0.500000 0.500000 0.500000
-0.500000 -0.500000 0.500000
However, I noticed that with ibrav=0 and
CELL_PARAMETERS
1.0 0.0 0.0
0.0 1.0 0.0
0.0 0.0 1.0
using the vectors of a simple cubic material and ntyp =2 at atomic
postions 0,0,0 and 1/2,1/2,1/2, the structure is seen as BCC from xcrysden.
I desire to use ibrav=0 and the lattice vectors of a BCC crystal.
I will sincerely appreciate any comment that can help me proceed with my
calculation.
Thank you.
Jolayemi Omamuyovwi RIta
Research Student
University of Benin
Nigeria.
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Lorenzo Paulatto - Paris
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