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Dear sir,<br>
<br>
Thank you for your detailed explanation. My understanding on the TS
is improved.<br>
<br>
best<br>
<br>
vega<br>
<br>
On 09/30/10 16:21, Stefano Baroni wrote:
<blockquote cite="mid:2B6F3476-5E4E-4828-B54B-6F39114BFBC6@sissa.it"
type="cite"><br>
<div>
<div>On Sep 29, 2010, at 5:32 PM, vega lew wrote:</div>
<br class="Apple-interchange-newline">
<blockquote type="cite">
<div bgcolor="#ffffff" text="#000000"> Through the relaxation
of a oxygen molecule on a surface by QE4.2, it dissociated
and adsorbed on the surface. The scf energy of each step has
decreased in compared with the previous step until the
relaxation completed. Now, can one say that there is not any
TS for O2 dissociation here ? <br>
<br>
<blockquote type="cite"> Probably not. The potential energy
surface might be not very corrugated and the energy
barrier for the dissociation might be not very large, so
that the dissociation of O2 could happen in a relax
calculation. I think there might be a very minute TS in
the dissociation process.<br>
</blockquote>
</div>
</blockquote>
<div><br>
</div>
here, I beg to differ. If a state, say B, can be reached from
another state, say A, following a path along which the energy
always decreases, this means *by definition* that there is *no*
energy barrier between A and B. I admit that if the energy
barrier is so "minute" as to be smaller that the numerical
accuracy of the minimization algorithm, it can escape proper
detection. (notice that this can be said of most, if not all,
numerical computations of any quantity)</div>
<div><br>
<blockquote type="cite">
<div bgcolor="#ffffff" text="#000000"> <br>
Or is the reaction spontaneous ? <br>
</div>
</blockquote>
<div><br>
</div>
It is spontaneous</div>
<div><br>
<blockquote type="cite">
<div bgcolor="#ffffff" text="#000000">
<blockquote type="cite">If the total energy of system goes
down continuously and the adsorption energy of dissociated
state is lower than the one of molecular state, you could
say the reaction is favorable. Whether it is spontaneous,
it is depend on how large of the energy barrier.<br>
</blockquote>
</div>
</blockquote>
<div><br>
</div>
in the reported conditions, the energy barrier is zero</div>
<div><br>
<blockquote type="cite">
<div bgcolor="#ffffff" text="#000000">
<blockquote type="cite">If there was a TS in this procedure
(dissociation and adsorption of O2) would the optimization
algorithm of QE4.2 stop the work or continue ? <br>
</blockquote>
</div>
</blockquote>
<div><br>
</div>
In the presence of an energy barrier, the system would stay
stuck in the starting configuration</div>
<div><br>
</div>
<div>Stefano</div>
<div> <br>
<blockquote type="cite">
<div bgcolor="#ffffff" text="#000000">If there is only one
bond broken in the process you considered, you could try
constrained optimization technique. For you information,
please refer to B.Hammer (Hammer, B.; Jacobsen, K. W.;
Norskov, J. K. Phys. Rev. Lett. 1992, 69, 1971) or PJ Hu's
work. (Alavi, A.; Hu, P.; Deutsch, T.; Silvestrelli, P. L.;
Hutter, J. Phys. Rev. Lett. 1998, 80, 3650). Or recent
developed method by ZP Liu (J. Chem. Theory Comput. 2010, 6,
1136–1144 )<br>
</div>
</blockquote>
<div><br>
</div>
If I have not misunderstood some important point, no constrained
minimization or other advanced techniques are needed here.</div>
<div><br>
</div>
<div>Stefano B</div>
<div><br>
</div>
<div>
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<div style="word-wrap: break-word;"><span
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<div style="word-wrap: break-word;">
<div>
<div style="margin: 0px;"><font
class="Apple-style-span" size="3"><span
class="Apple-style-span"
style="font-size: 12px;">---</span></font></div>
<div style="margin: 0px;"><font
class="Apple-style-span" size="3"><span
class="Apple-style-span"
style="font-size: 12px;">Stefano
Baroni - SISSA</span></font><font
class="Apple-style-span" size="3"><span
class="Apple-style-span"
style="font-size: 12px;"> </span></font><font
class="Apple-style-span" size="3"><span
class="Apple-style-span"
style="font-size: 12px;">&</span></font><font
class="Apple-style-span" size="3"><span
class="Apple-style-span"
style="font-size: 12px;"> </span></font><font
class="Apple-style-span" size="3"><span
class="Apple-style-span"
style="font-size: 12px;">DEMOCRITOS
National Simulation Center - Trieste</span></font></div>
<div style="margin: 0px;"><font
class="Apple-style-span" size="3"><span
class="Apple-style-span"
style="font-size: 12px;"><a
moz-do-not-send="true"
href="http://stefano.baroni.me">http://stefano.baroni.me</a>
[+39] 040 3787 406 (tel) -528 (fax) /
stefanobaroni (skype)</span></font></div>
<div style="margin: 0px; font: 12px
Helvetica; min-height: 14px;"><br
style="font-size: 12px;">
</div>
<div style="margin: 0px; font: 12px
Helvetica; min-height: 14px;"><span
class="Apple-style-span"
style="font-size: 14px;">
<div style="margin: 0px;"><font
class="Apple-style-span" size="3"><span
class="Apple-style-span"
style="font-size: 12px;">La morale
est une logique de l'action comme
la logique est une morale de la
pensée - Jean Piaget</span></font></div>
<div style="margin: 0px;"><font
class="Apple-style-span" size="3"><span
class="Apple-style-span"
style="font-size: 12px;"><br>
</span></font></div>
</span></div>
<div style="margin: 0px;"><font
class="Apple-style-span" size="3"><span
class="Apple-style-span"
style="font-size: 12px;">Please, if
possible, don't</span></font><font
class="Apple-style-span" size="3"><span
class="Apple-style-span"
style="font-size: 12px;"> </span></font><font
class="Apple-style-span" size="3"><span
class="Apple-style-span"
style="font-size: 12px;">send me MS
Word or PowerPoint attachments</span></font></div>
<div style="margin: 0px;"><font
class="Apple-style-span" size="3"><span
class="Apple-style-span"
style="font-size: 12px;">Why? See:</span></font><font
class="Apple-style-span" size="3"><span
class="Apple-style-span"
style="font-size: 12px;"> </span></font><font
class="Apple-style-span" color="#0023e9"
size="3"><span class="Apple-style-span"
style="font-size: 12px;"><a
moz-do-not-send="true"
href="http://www.gnu.org/philosophy/no-word-attachments.html">http://www.gnu.org/philosophy/no-word-attachments.html</a></span></font></div>
<div><font class="Apple-style-span"
color="#0023e9" size="3"><span
class="Apple-style-span"
style="font-size: 12px;"><br
class="webkit-block-placeholder">
</span></font></div>
</div>
</div>
</span><br class="Apple-interchange-newline">
</div>
</span><br class="Apple-interchange-newline">
</div>
</span><br class="Apple-interchange-newline">
</div>
</span><br class="Apple-interchange-newline">
</span><br class="Apple-interchange-newline">
</div>
<br>
<pre wrap="">
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</blockquote>
<br>
<div class="moz-signature">-- <br>
<p><font color="black">
================================================<br>
Vega Lew ( weijia liu)<br>
Graduate student<br>
State Key Laboratory of Materials-oriented Chemical
Engineering<br>
Nanjing University of Technology, 210009, Nanjing, China<br>
***************************************************************<br>
Email: <a class="moz-txt-link-abbreviated" href="mailto:vegalew@gmail.com">vegalew@gmail.com</a><br>
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