Hello Marzieh,
I took the freedomn to use your data to test a little fitting procedure
I just wrote. I tried to fit parameters a, b, c of the function
y=a(x-b)**2+c
to your data.
The fit crashed - probably like the one you may have used - when
presented the data and asked to fit the parabola from scratch. The
reason for such a behaviour of a fit procedure frequently is bad user
behaviour: The program is quite understandably unable to guess
reasonable starting values for the fit parameters from such data.
Presented with starting values
a=1.000000e-06, b=9.500000e+03, c=-8.857000e+04
the fit finds without complaining a very good fit with
a=5.687893e-07, b=9.612186e+03, c=-8.856770e+04
So you should do your DFT volume optimization around a volume of 9612 -
and probably give a little thought to the problem of why you started so
far off the optimum at larger volumes.
Good luck
Martin Pieper
---
Dr. Martin Pieper
Karl-Franzens University
Institute of Physics
Universitätsplatz 5
A-8010 Graz
Austria
Tel.: +43-(0)316-380-8564
Am 09.09.2015 03:43, schrieb Marzieh Gh:
Dear Prof.Blaha & Tran
I have calculated optimization of supercell (1*1*2). But Energy vs
Volume is linear!
case.outputeos:
10575.3364 -88567.151612
11162.8553 -88566.366642
12925.4112 -88561.471064
11750.3745 -88565.095045
12337.8929 -88563.437182
Is this normal? If no what is reason? What do I do?
Please help me
Best Regards
--
Marzieh Ghoohestani
PhD Student of Computational Nano Physics
Nano Research Center, Department of Physics
University of Technology, Isfahan, Iran
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