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Hey,<br>
<br>
I'm a newbie too and I'm wondering how can you equilibrate the
lattice constant by doing just a scf calculation.<br>
Also, it seems to me that only MD is able to reproduce experimental
data since it takes into account the temperature and the pressure.<br>
Please, let me know if I'm wrong.<br>
<br>
Eric.<br>
<br>
On 03/02/2011 05:58 PM, Krukau, Aliaksandr wrote:
<blockquote
cite="mid:20110302175819.hkx8o4qh88ww40cw@webmail.iu.edu"
type="cite">
<pre wrap=""> Dear QE users,
I apologize if my question seems stupid to you. I am a complete QE newbie
and could not find any answer in the tutorials.
I am trying to find equilibrium lattice constant for copper with PBE
and ultrasoft pseudopotentials. I ran scf calculations for face-centered cubic
unit cell for a number of lattice constants:
Lattice constant 6.65 a.u. ! total energy =
-121.62734203 Ry
Lattice constant 6.66 a.u. ! total energy =
-121.62735421 Ry
Lattice constant 6.67 a.u. ! total energy =
-121.62734651 Ry
Lattice constant 6.65 a.u. ! total energy =
-121.62731956 Ry
The minimum total energy is for the lattice constant 6.66 a.u.
But this value drastically differs from the published PBE value of 6.86 a.u.
(Phys. Rev. B, vol. 77, 05414 (2008), Table II). It also differs from
the experimental value of 6.83 a.u. I attach the input file that I used
for lattice constant 6.66 a.u. below the signature.
Why is equilibrium lattice constant so low?
Best regards,
Alex Krukau,
Indiana University
------------------------------------------------------
&control
calculation='scf'
pseudo_dir = '~/espresso-4.2.1/pseudo/ADDITIONAL',
/
&system
ibrav = 2,
celldm(1) = 6.66,
nat= 1,
ntyp= 1,
ecutwfc = 120.0,
ecutrho = 1000.0
occupations='smearing', smearing='marzari-vanderbilt', degauss=0.01
/
&electrons
conv_thr=0.0000001
/
ATOMIC_SPECIES
Cu 63.546 Cu.pbe-n-van_ak.UPF
ATOMIC_POSITIONS
Cu 0.0 0.0 0.0 1 1 1
K_POINTS automatic
12 12 1 0 0 0
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</pre>
</blockquote>
<br>
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<em>
Be the change you wish to see in the world<br>
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<br>
<a href="mailto:germaneau@gucas.ac.cn">Dr. Éric Germaneau</a><br>
<br>
College of Physical Sciences<br>
Graduate University of Chinese Academy of Sciences<br>
Yuquan Road 19A<br>
Beijing 100049<br>
China<br>
<br>
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