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On 07/05/2010 08:19 PM, Masoud Nahali wrote:
<blockquote cite="mid:COL114-W485EB4FCB4B3CF6013F592A1B10@phx.gbl"
type="cite">
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--></style>Dear
Quantum Espresso users<br>
<br>
I optimized the graphite bulk and the layers were completely flat. But
when I try to "relax" the graphite surface (slab 2*2 with 3 monolayer)
with 10 angstrom vacuum all the layers become extremely ripple!!! I can
not find the problem. May it related to the number of layers? anyhow
the number of layers is like the bulk. Your help would be a great gift.<br>
<u></u><br>
</blockquote>
Are you using the experimental or the theoretical value for the
in-plane (graphene) C-C distance? I guess that the PBE value is larger
than the experimental one, so that if you start from the experimental
C-C distance in the graphene layer and let everything relax, then the
atoms would like to go towards the theoretical equilibrium distance and
this may cause the rippled structure.<br>
Secondly, I don't know if you can pretend that the innermost layer is
graphite bulk-like, having only three layers in total.<br>
<br>
<br>
HTH<br>
<br>
GS <br>
<br>
<pre class="moz-signature" cols="72">--
Gabriele Sclauzero, EPFL SB ITP CSEA
PH H2 462, Station 3, CH-1015 Lausanne
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