<div dir="ltr">Hi,<div><br></div><div>Thank you very much for the answer. </div><div><br></div><div>Is k-points also the reason why I got incorrect distance between atoms and layers? How can I fix it? I tried adding KOINTS section in the DFT section, but it gives me following error message: "WFN based interpolation method not possible for kpoints."</div><div><br></div><div>Thank you very much!</div><div><br></div><div>Chenxing<br><br><br><blockquote class="gmail_quote" style="margin: 0;margin-left: 0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;">Hi
<br>
<br>my guess is, that you see the effect of incomplete sampling of
<br>the Brillouin zone. By using different supercells you get
<br>different back folding of the reciprocal cell. It is like using
<br>more or less appropriate k-points.
<br>
<br>regards
<br>
<br>Juerg Hutter
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<br>From: Chenxing Yang 
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<br>Date: 04/01/2017 05:21AM
<br>Subject: [CP2K:8891] geometry optimization for graphite
<br>
<br>Dear All,
<br>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.
<br>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?
<br>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. 
<br>Here is my input file attached. Thank you very much!
<br>Kind regards,
<br>Chenxing Yang
<br>
<br>
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<br>[attachment "graphite.inp" removed by Jürg Hutter/at/UZH]
<br></blockquote></div></div>