<html>
<head>
<meta content="text/html; charset=windows-1252"
http-equiv="Content-Type">
</head>
<body text="#000000" bgcolor="#FFFFFF">
<div class="moz-cite-prefix">Dear Niels,<br>
<br>
are you sure the two cells are equivalent?<br>
Are the results of the two cells still different if you remove the
dipole correction?<br>
In your message you say the in-plane stresses are different, and
in the subsequent line you say they are equal... What exactly is
different and what is equal?<br>
<br>
best,<br>
stefano<br>
<br>
On 02/09/2015 10:17, Niels Walet wrote:<br>
</div>
<blockquote
cite="mid:EFA9346E0B58924D89F3354CB3817D735BECB08D@MBXP02.ds.man.ac.uk"
type="cite">
<meta http-equiv="Content-Type" content="text/html;
charset=windows-1252">
<style id="owaParaStyle" type="text/css">P {margin-top:0;margin-bottom:0;}</style>
<div style="direction: ltr;font-family: Tahoma;color:
#000000;font-size: 10pt;">I have tried to run a geometry
optimisation on a 2D water slab using VDW-DF exchange
functional, dipole correction, etc., etc.<br>
<br>
I find that by starting from different initial states, I can end
up with two equivalent supercells, one of which has a
rectangular basis, and the other has a parallelogram as base
(angle about 60 degrees). The total energies after minimisation
agree to 7 decimal places. So far so good. The in-plane stresses
are very different, however: the rectangular one is 2.7 GPa, and
the parallelogram one is 2.2 GPa (both in plane stresses are
equal as one would expect).
<br>
<br>
Is there any reason why that should be the case? Anyone aware of
any pitfalls with the calculation of stresses in the vdW part of
the code? I am using QE 5.1.2.<br>
<br>
Niels<br>
<div><br>
<div style="font-family:Tahoma; font-size:13px">
<div style="font-family:Tahoma; font-size:13px"><font
style="font-family:Helvetica" size="2"><span
style="font-size:10pt">---<br>
Prof. Niels R. Walet
Phone: +44(0)1613063693<br>
School of Physics and Astronomy Fax:
+44(0)1613064303<br>
The University of Manchester Mobile:
+44(0)7516622121<br>
Manchester, M13 9PL, UK room 7.7,
Schuster Building<br>
email: <a class="moz-txt-link-abbreviated" href="mailto:Niels.Walet@manchester.ac.uk">Niels.Walet@manchester.ac.uk</a><br>
web: <a moz-do-not-send="true"
href="../../owa/redir.aspx?C=8f9098c1943846dcba17536b8618a38a&URL=http%3a%2f%2fwww.theory.physics.manchester.ac.uk%2f%7emccsnrw"
target="_blank">
http://www.theory.physics.manchester.ac.uk/~mccsnrw</a></span></font></div>
</div>
</div>
</div>
<br>
<fieldset class="mimeAttachmentHeader"></fieldset>
<br>
<pre wrap="">_______________________________________________
Pw_forum mailing list
<a class="moz-txt-link-abbreviated" href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a>
<a class="moz-txt-link-freetext" href="http://pwscf.org/mailman/listinfo/pw_forum">http://pwscf.org/mailman/listinfo/pw_forum</a></pre>
</blockquote>
<br>
</body>
</html>