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<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>
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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).
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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>
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Niels<br>
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<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: Niels.Walet@manchester.ac.uk<br>
web: <a 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>
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