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Hello Maxime,<br>
<br>
Thank you for the detailed answer. I will have a look at DFTB+
software.<br>
<br>
Regarding cp2k, if I understand well, it is better so far to only
use the scc and non-scc parameters which are provided within the
data section of the code and not the more advanced parameters found
on DFTB website.<br>
<br>
Regards,<br>
Pierre<br>
<br>
<div class="moz-cite-prefix">On 27/02/2020 09:12, Maxime Van den
Bossche wrote:<br>
</div>
<blockquote type="cite"
cite="mid:4fed78db-4d46-4d...@googlegroups.com">
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<div dir="ltr">
<div>Hello again,</div>
<div><br>
</div>
<div>I had a closer look at the <a
href="http://www.dftb.org/parameters/download/3ob/3ob-3-1-cc/"
moz-do-not-send="true">3ob parameter set</a> and it seems
like not all the</div>
<div>'bells and whistles' have been implemented in the DFTB
module in CP2K</div>
<div>to make proper use of this parametrization:</div>
<div><br>
</div>
<div>- It is supposed to be used with 'full' third-order terms,
not just the diagonal ones</div>
<div>(note: there are also the LMAX_DFTB and DFTB3_PARAM
keywords which</div>
<div>need to be set under CP2K_INPUT/FORCE_EVAL/SUBSYS/KIND).</div>
<br>
<div>- Becke-Johnson damping of the D3 correction doesn't seem
available in the</div>
<div>DFTB module (though it is available for e.g. DFT
calculations).</div>
<div><br>
</div>
<div>The simplest way to deal with this, I think, is to use the
DFTB+ code instead of</div>
<div>CP2K. As an example, I have attached a ZIP file with DFTB+
input files and the</div>
<div>final geometry I got out of it. There is a +20% expansion
in the c-direction.</div>
<div>I have no real experience with DFTB calculations of
molecular crystals, so I don't</div>
<div>know if this is a typical deviation or not. Where did the
initial geometry come from?</div>
<div><br>
</div>
<div>/Maxime<br>
</div>
</div>
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<br>
<pre class="moz-signature" cols="72">--
Dr Pierre Cazade, PhD
AD3-023, Bernal Institute,
University of Limerick,
Plassey Park Road,
Castletroy, co. Limerick,
Ireland</pre>
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