[CP2K:8891] geometry optimization for graphite

[hut... at chem.uzh.ch]

Hi

my guess is, that you see the effect of incomplete sampling of
the Brillouin zone. By using different supercells you get
different back folding of the reciprocal cell. It is like using
more or less appropriate k-points.

regards

Juerg Hutter
--------------------------------------------------------------
Juerg Hutter                         Phone : ++41 44 635 4491
Institut für Chemie C                FAX   : ++41 44 635 6838
Universität Zürich                   E-mail: hut... at chem.uzh.ch
Winterthurerstrasse 190
CH-8057 Zürich, Switzerland
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-----cp... at googlegroups.com wrote: -----To: cp2k <cp... at googlegroups.com>
From: Chenxing Yang 
Sent by: cp... at googlegroups.com
Date: 04/01/2017 05:21AM
Subject: [CP2K:8891] geometry optimization for graphite

Dear All,
I have run some simulations of geometry optimization for graphite with OPT-PBE using CP2K 4.1, and I have some problem on reproducing the correct crystalline structure of graphite.
For some reason, the bond length is slightly overestimated (1.448 Å), and inter-layer distance is underestimated (2.756 Å), where experiment results are 1.421 Å and 3.33 Å. It seems those 2 distances can be very well reproduced using OPT-PBE in the literature. Could you please help me to check if something is wrong in the input file?
Another problem I encountered is, if I simulate in a 3*3*3 supercell, the atoms is located same position of atoms in the adjacent layer, instead of centre of hexagon, but it is fine if the supercell is set as 2*2*2 and 4*4*4. 
Here is my input file attached. Thank you very much!
Kind regards,
Chenxing Yang



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[attachment "graphite.inp" removed by Jürg Hutter/at/UZH]