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You provide very poor information concerning your calculation. As a
consequence it appears difficult to help you. <br>
I can simply say that if you have used a supercell 2a x 2b x c, then
a' = 2a = 7.18 A° at the beginning. <br>
<br>
If after the geometry optimization you have obtained a' = 7.5 A°, it
means that a' is overestimated by about 4.4%. <br>
<br>
We expect an overestimation of the cell parameters from GGA, and
underestimation from LDA. I imagine that you have selected GGA for
your geometry optimization. <br>
<br>
Concerning the experimental value a = 3.59 A°, i.e. a' = 2a = 7.18
A°, is it the dimension of the alloy or the dimension related to a
pure phase (neglecting the impact of the substituent elements)? <br>
<br>
Regards<br>
<br>
Xavier<br>
<br>
<br>
<br>
On 04/18/2012 05:03 PM, ben amara imen wrote:
<blockquote
cite="mid:CACAZvnr_GgVAkD6u73DvLNq_1dgWr2MWMoH-so08PvfekZDGog@mail.gmail.com"
type="cite">
<div dir="ltr">Hello! <br>
i'm trying to use supercell in order to determine electronic
structure for ternary alloy.<br>
When i have generated 2*2*1 supercell , i have noted that the
new lattices parameters (a,b,c) are very large camparatively
with the starting lattices parameters<br>
for exp: a=3.59 A° , with supercell, a will be 7.5A° !!!! <br>
Also i do the optimization BUT the value still large<br>
It's normal and correct what i have found , if not what's the
problem???<br>
can you help me please and thanks in advance<br>
<br>
</div>
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