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<p><tt>two things I think might be the origin of strange results.</tt></p>
<p><tt> </tt></p>
<p><tt>your ethyl-anion is charged. the code introduce a
compensating background that should cancel out when you calculate
the adsortion energy but you are using different cells in the
two charged configurations. so something does not cancel out as
it should.</tt></p>
<p><tt> </tt></p>
<p><tt>there might be some vdW interaction contributing to the
physisorption. I see no inclusion of vdW corrections or use of
vdW-aware functionals in your calculations. <br>
</tt></p>
<p><tt><br>
</tt></p>
<p><tt>best<br>
</tt></p>
<p><tt><br>
</tt></p>
<p><tt>stefano</tt><br>
</p>
<br>
<div class="moz-cite-prefix">On 08/03/2018 15:50, Laurens Siemons
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:AM6PR10MB200779A59AFB6EB79A0396C7BBDF0@AM6PR10MB2007.EURPRD10.PROD.OUTLOOK.COM">
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<div>Dear all,
<p style="margin-top:0; margin-bottom:0"><br>
</p>
<p style="margin-top:0; margin-bottom:0">I'm calculating
parameters like adsorption energy, geometric parameters, NMR
chemical shifts of adsorbates on a surface. In this specific
case I calculated the adsorption energy of an ethyl anion on
an anatase 001 surface of titania. I got the following
energies:</p>
<p style="margin-top:0; margin-bottom:0"><br>
</p>
E<sub>surface + adsorbate </sub>= <span>-4301.05337244</span>
<p style="margin-top:0; margin-bottom:0">E<sub>surface </sub>=
<span>-4258.9387474</span><br>
</p>
<p style="margin-top:0; margin-bottom:0">E<sub>adsorbate </sub>=
<span>-42.37757742</span><br>
</p>
<p style="margin-top:0; margin-bottom:0"><br>
</p>
<p style="margin-top:0; margin-bottom:0">So E<sub>ads </sub>=
<span>E<sub>surface + adsorbate</sub></span> - (E<sub>surface
</sub>+ E<sub>adsorbate</sub>) = 0.26<br>
</p>
<p style="margin-top:0; margin-bottom:0"><br>
</p>
<p style="margin-top:0; margin-bottom:0">Now this seems wrong.
If E<sub>ads</sub> is positive, so adsorption is not
favourable, then the ethyl-anion should migrate away from
the surface in the relax calculation of a001cti. correct? I
executed the three calculations with the exact same
parameters as the other ones so I don't see how this is
possible. I attached my input files of the calculations. I
hope someone can guide me through this.</p>
<p style="margin-top:0; margin-bottom:0"><br>
</p>
<p style="margin-top:0; margin-bottom:0">Thanks in advance,</p>
<p style="margin-top:0; margin-bottom:0">Laurens Siemons</p>
<p style="margin-top:0; margin-bottom:0">Master student
chemistry</p>
University of Antwerp</div>
<br>
</div>
<br>
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