<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta content="text/html; charset=ISO-8859-1"
http-equiv="Content-Type">
<title></title>
</head>
<body text="#000000" bgcolor="#ffffff">
On 07/13/2010 12:49 PM, Masoud Nahali wrote:
<blockquote
cite="mid:AANLkTilAnhIzjqbPiAvK-KuqhH1l_k_j7YWOUGRtlPIS@mail.gmail.com"
type="cite">
<div> Dear Gabriele Sclauzero and pwscf Users</div>
<div> </div>
<div> Many thanks for your attentions. The cell dimension and
the positions of the atoms are exactly correct. </div>
</blockquote>
<br>
Are you completely sure? You can find as an attachment a picture (from
xcrysden) of the central graphene layer according to the positions
given in your input. You can now judge if it looks like a honeycomb
lattice.<br>
<br>
<blockquote
cite="mid:AANLkTilAnhIzjqbPiAvK-KuqhH1l_k_j7YWOUGRtlPIS@mail.gmail.com"
type="cite">
<div>Yes, indeed the high ecutrho is important for ultrasoft
pseudopotentials. About the rippling : It was my mistake in selecting a
wrong pseudopotential which has a hole. Nicola had explained it before
and accordingly I solved it. The graphite surface is not ripple. When I
use the "max_second=6000 and dt=150" the job completes very fast as the
example of pwscf. Is the using of such keyboards plausible?</div>
</blockquote>
<br>
Please spend some time reading Doc/INPUT_PW to understand the meaning
of the _keywords_. dt is used only for molecular dynamics runs, not
relaxations, while max_seconds has nothing to do with how fast your job
is completed.<br>
<br>
<br>
GS<br>
<blockquote
cite="mid:AANLkTilAnhIzjqbPiAvK-KuqhH1l_k_j7YWOUGRtlPIS@mail.gmail.com"
type="cite">
<div> As I mentioned before I had used the optimized cell parameters
of (1*1 slab) for vc-relaxing the (2*2 slab) and I expected to see the
results very soon but the calculation was time consuming while there
was only a very very bit change of the cell dimensions during this 16
hours. There is only 1-3 iterations per each step in the output file
and each of them was time consuming. The job was completed after about
50 steps. </div>
<div class="gmail_quote">
<div> </div>
<div>-------------------------------------------------------------------------</div>
<blockquote class="gmail_quote"
style="border-left: 1px solid rgb(204, 204, 204); margin: 0px 0px 0px 0.8ex; padding-left: 1ex;">Dear
Masoud,<br>
<br>
first I would suggest you to use bfgs as the algorithm for both ions
and cell dynamics. Excepted particular cases, it should reach the
minimum much faster.<br>
<br>
Also, why do you specify the cell with such an unusual way. You simply
need celldm(1) and celldm(3) with ibrav=4 if you want to describe an
hexagonal lattice. Other suggestions: your ecutrho looks really large
to me, do you really need it. On the other hand, degauss might be too
large to describe a spin-polarized system.<br>
<br>
Then, are you sure that you have built correctly your supercell? It
looks like there are some C-C bonds much shorter that others in the
central graphene plane (1.2 instead of 1.4 angs). Please check again
your structure.<br>
In general, you can expect that if you relax the atoms in the supercell
some kind of surface-reconstruction may appear, since you leave more
freedom to atoms to rearrange in structures with larger periodicity. I
don't think this is the case for graphite, but you may find some
ripples (as you mentioned in your earlier emails, if I am not wrong) if
the C-C bonds are at a distance shorter than the theoretical
equilibrium distance (I guess).<br>
<br>
HTH<br>
</blockquote>
<div>------------------------------------------------------------------------------------------------<br>
Dear Quantum Espresso Users<br>
><br>
> I vc-relaxed a (1*1) slab of graphite surface with 3 layers; It
takes 20 minutes with parallel running by 4 CPUs. Then I used the exact
optimized cell parameters (obtained from vc-relaxed calculation) to
make a (2*2) slab of graphite with 3 layers and I expected to see the
results in a few minutes. But amazingly it took 17 hours to complete.
48 steps were done in the calculation for vc-relaxing the cell which
have the parameters that had been optimized before. The cell parameters
only change a very bit in the current vc-relaxing the (2*2) slab. I
appreciate if one explain the physical procedure of vc-relaxing and the
reason of the time needed for the computation.<br>
><br>
> input file:<br>
><br>
> CONTROL<br>
> calculation = "vc-relax",<br>
> pseudo_dir = "/home/koa/soft/qe4.2/<br>
> espresso-4.2/pseudo",<br>
> outdir = "/home/koa/tmp",<br>
> etot_conv_thr= 1.0D-4,<br>
> forc_conv_thr= 1.0D-3,<br>
> dt=80,<br>
> /<br>
> &SYSTEM<br>
> ibrav = 4,<br>
> a = 2.4579,<br>
> b = 2.4579,<br>
> c = 16.3069,<br>
> cosab = -0.5,<br>
> cosac = 1.0,<br>
> cosbc = 1.0,<br>
> nat = 6,<br>
> ntyp = 1,<br>
> ecutwfc = 40.D0,<br>
> ecutrho = 480.D0,<br>
> occupations = 'smearing'<br>
> smearing ='mp',<br>
> degauss = 0.03,<br>
> nspin = 2,<br>
> starting_magnetization(1)= 0.003,<br>
> london=.true.,<br>
> /<br>
> &ELECTRONS<br>
> conv_thr = 1.D-6,<br>
> mixing_beta = 0.7D0,<br>
> diagonalization = "david",<br>
> /<br>
> &IONS<br>
> ion_dynamics="cg"<br>
> /<br>
> &CELL<br>
> cell_dynamics = 'damp-w',<br>
> press = 0.0,<br>
> /<br>
> ATOMIC_SPECIES<br>
> C 12.0107 C.pbe-rrkjus.UPF<br>
> ATOMIC_POSITIONS {angstrom}<br>
> C 0.00000000 0.00000000 0.00000000 1 1 0<br>
> C 0.00000000 1.41908472 0.00000000<br>
> C 0.00000000 0.00000000 3.15347111<br>
> C 11.22896342 0.70954236 3.15347111<br>
> C 0.00000000 0.00000000 6.30694222<br>
> C 0.00000000 1.41908472 6.30694222<br>
> K_POINTS {automatic}<br>
> 4 4 1 1 1 1<br>
><br>
</div>
<div> Sincerely Yours<br>
Masoud Nahali<br>
SUT<br>
<br>
</div>
</div>
<pre wrap="">
<fieldset class="mimeAttachmentHeader"></fieldset>
_______________________________________________
Pw_forum mailing list
<a class="moz-txt-link-abbreviated" href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a>
<a class="moz-txt-link-freetext" href="http://www.democritos.it/mailman/listinfo/pw_forum">http://www.democritos.it/mailman/listinfo/pw_forum</a>
</pre>
</blockquote>
<br>
<br>
<pre class="moz-signature" cols="72">--
Gabriele Sclauzero, EPFL SB ITP CSEA
PH H2 462, Station 3, CH-1015 Lausanne
</pre>
</body>
</html>