Dear Savita,<br><br>It is hard to tell....You can try plotting total energy vs. the box size and see how the energies are changing....if the change is of the order of a meV then I would say that your calculations are converged wrt box size.......<br>
<br>However, I think it is good idea to follow Stefano's suggestion........using the same basis set you have been using for your mp2 calculation, you try to calculate the same thing using DFT and see whether you get similar results.....if you get different results, then it will suggest that DFT is not properly describing the electronic correlations. <br>
<br>Prasenjit<br><br><div class="gmail_quote">On 20 June 2011 10:24, <span dir="ltr"><<a href="mailto:psavita@crlindia.com">psavita@crlindia.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<font face="Default Sans Serif,Verdana,Arial,Helvetica,sans-serif" size="2"><div>Dear Prof. Ghosh,<br><br>As per your suggestion, I performed the structure relaxation of LiH--H2O system using a bigger cubic box of dimension 50 a.u.<br>
and I still find H2 abstraction instead of an intramolecular dihydrogen bond.<br>Do you think the box is still inadequate?<br>For such systems, would it be better to put some constraints initially?<br>How do we do this in QE?<br>
<br>Thanks for your suggestion and best regards,<br><br></div><div><div class="im"><font face="Default Sans Serif,Verdana,Arial,Helvetica,sans-serif" size="2"><div><font style="font-family: Georgia,Default Serif,serif; font-weight: bold;" color="#0000ff"><font color="#999900">Savita Pundlik</font></font><br style="font-family: Georgia,Default Serif,serif;">
<span style="font-family: Georgia,Default Serif,serif;"><font><font color="#999900">Computational Materials </font></font></span><font color="#999900">Applied Research Group</font><br style="font-family: Georgia,Default Serif,serif;">
<span style="font-family: Georgia,Default Serif,serif; font-weight: bold;"><font><font color="#999900">Computational Research Laboratories Ltd.,</font></font></span><br style="font-family: Georgia,Default Serif,serif;"><span style="font-style: italic; font-family: Georgia,Default Serif,serif;"><font><font color="#999900">Taco House, Damle Path, Off Law College Road</font></font></span><br style="font-style: italic; font-family: Georgia,Default Serif,serif;">
<span style="font-style: italic; font-family: Georgia,Default Serif,serif;"><font><font color="#999900">Pune - 411004, India.</font></font></span><br><br></div></font><br><div><br></div></div><font color="#990099">-----<a href="mailto:pw_forum-bounces@pwscf.org" target="_blank">pw_forum-bounces@pwscf.org</a> wrote: -----<br>
<br></font><blockquote style="border-left: 2px solid rgb(0, 0, 0); padding-right: 0px; padding-left: 5px; margin-left: 5px; margin-right: 0px;"><font face="Courier New,Courier,monospace" size="3"><div class="im"><br><br><br>
<br><br>Dear Savita,<br><br>I am not an expert on these type of systems.......however just a small piece<br>of advice.....a single molecule of water has a huge dipole moment.....so a<br>box size of 25 bohr may not be sufficient, until and unless binding to LiH<br>
quenches the dipole moment......so you may like to check whether your box is<br>sufficiently big.....usually for a single molecule of water one uses about<br>35-40 bohr box or can use dipole correction.<br><br>Prasenjit<br>
<br>On 17 June 2011 11:42, <a href="mailto:psavita@crlindia.com" target="_blank"><psavita@crlindia.com></a> wrote:<br><br>> Hello,<br>><br>> I have been trying to get the optimum structure of LiH..H2O that has an<br>
> intramolecular dihydrogen bond, using pwscf.<br>> I could get the proper structure earlier using mp2 theory and 6-31++g<br>> basis.<br>><br>> For pwscf, the species is enclosed in a cubic box of 25 bohr for gamma<br>
> point calculation.<br>> I tried the pz lda, pbe gga as well we blyp PS for the atoms in this<br>> system, however, the first and the last<br>> lead to H2O..LiH, the latter LiH being linear while pbe gives LiH + H2, but<br>
</div>> no dihydrogen bond. Is there any other PS<div class="im"><br>> that may lead to proper structure? Or is it that plane wave approach does<br>> not suit systems of this kind?<br>><br></div><div class="im">
> Thanks in advance and best regards,<br>><br>> Savita Pundlik<br>> Computational Materials Applied Research Group<br>> Computational Research Laboratories Ltd.,<br>> Taco House, Damle Path, Off Law College Road<br>
> Pune - 411004, India.<br>><br>><br>><br>> _______________________________________________<br></div><div class="im">> Pw_forum mailing list<br>> <a href="mailto:Pw_forum@pwscf.org" target="_blank">Pw_forum@pwscf.org</a><br>
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IISER Pune,<br>First floor, Central Tower, Sai Trinity Building<br>Garware Circle, Sutarwadi, Pashan<br>Pune, Maharashtra 411021, India<br><br>Phone: +91 (20) 2590 8203<br>Fax: +91 (20) 2589 9790<br></div>-------------- next part --------------<br>
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<br></blockquote></div><br><br clear="all"><br>-- <br>PRASENJIT GHOSH,<br>Assistant Professor,<br>IISER Pune,<br>First floor, Central Tower, Sai Trinity Building<br>Garware Circle, Sutarwadi, Pashan<br>Pune, Maharashtra 411021, India<br>
<br>Phone: +91 (20) 2590 8203<br>Fax: +91 (20) 2589 9790<br>