Dear Douglas,
To get a fairly accurate cohesive energy with LDA, even with GGA
functionals, is challenging yet.
We had a discussion recently on the simulated Ecohes of Fe in this
mailing list, which is rather bad. I tried to improve the situation,
and I implemented Wigner's type correlation functionals into SIESTA,
which give very good values for atoms and small molecules. Indeed, I got
improved values for Fe. However, I'm not sure, that this performance holds
for other materials.
Anyhow, you should not worry about the difference you have mentioned
for Cu3Au, I would say it is not bad. ~1 eV/atom difference could easily
be occurred with present day xc functionals.
Hybrid functionals, which incorporates exact exchange could be better,
however, this option is not available in SIESTA.
Best regards, Peter Sule
----------------------------------------------------
Dr. Peter Sule
senior research associate
Institue for Technical Physics and Materials Science
(MTA-MFA), Konkoly-Thege M. 29-33, Budapest, Hungary
tel.: (36) 1 392 2222/3605
fax.: (36) 1 392 22 73
www.mfa.kfki.hu/~sule / [email protected]
-----------------------------------------------------
On Thu, 27 May 2010, [email protected] wrote:
Hello, my name is Douglas Martins and I am a doctoral student at UFJF-Brazil.
I'm starting to work with the SIESTA to calculate the cohesive energy of the
alloy Cu3Au,
I did the calculation for the league and then to the Au and Cu atoms alone,
then
subtracts the energy of the alloy Cu3Au the energies of Au and three times
the energy Cu.
But I got a value
4.86 ev, but experimentally this value is 3.64 ev. I wonder if anyone knows
how to make
that calculation of cohesion energy correctly or if there is better value in
this energy
arquivo.out output. If someone can get me well as they should be the input
parameters for
the league and the atoms apart, I would greatly appreciate it.
A big hug to everyone and I await the return.
Graciously
Douglas
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