[CP2K-user] [CP2K:11565] Graphite MD on cp2k

[Patrick Gono]

Dear Sasawat,

I have looked at your input files, and ran some calculations of my own. My
graphite seems to behave well, but I did not run the MD for a long time
(see fiel attached). However, without the .xyz files you used for your
simulations, I can not be sure where the problem is.

Regarding the input files, you may consider adopting an orbital
transformation method (section &OT), as it generally performs faster than
diagonalization. I had no convergence issues in my tests using CG
minimizer, and DIIS may be even faster.

Next, and probably more important, you adopted quite a low value for the
cutoff. Generally, one should aim at higher triple digits. 200 Ry might be
too low for a reliable simulation result.

Finally, the 1x1x8 cell you use is very long and narrow. In the simulations
without k-points, this might lead to some unphysical behaviour, as your
simulation is not relaxed with respect to cell size. The 3x3x8 supercell
seems more reasonable.

Regardless, I need to ask you for your .xyz structures in order to nail
down the issue. If you have the computed MD trajectories, I'd like to see
them as well, in order to know after how many steps I can expect to observe
what you mentioned.

Yours sincerely,
Patrick Gono

On Sun, 14 Apr 2019 at 22:01, <sjam... at eng.ucsd.edu> wrote:

> Hello cp2k users,
>
> I am currently trying to run an MD simulation on 8 layers graphite to
> generate different snapshots at 300K. The simulation result showed layer
> separation and the carbon atoms were flying out from the unit cell as if
> it's vaporizing. So far I have done the calculation with PBE+DFTD3
> correction, a 3x3 unit cell in xy with RevPBE and DFTD3 correction and
> calculation with kpoints. None have worked out to produce a desired
> vibrational motion. Any advice would be appreciated.
>
> Best,
> Sasawat
>
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