<div dir="ltr"><div>Is the problem here the loss of the original symmetry of the lattice? if hexagonal symmetry was present in the starting structure, it isn't lost at the end (apart from pathological or unfortunate cases). If hexagonal symmetry was not present in the starting structure, the final lattice may no longer be hexagonal</div><div><br></div><div>Paolo<br></div><div><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sat, Mar 23, 2019 at 7:05 AM Bharat Thapa <<a href="mailto:bhathapa@gmail.com">bhathapa@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div><p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif">Dear developer, </p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"> </p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif">I have vc-relaxed Hf7O8N4 (hafnium oxynitride) assuming the
crystal to be rhombohedra with a=b, alpha=beta=90 deg, and gamma=120 deg. So, I
used ibrav=4 and gave A,B,C, cosAB, cosAC and cosBC values. Part of the input
looks as follows:</p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"> </p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><i>&system</i></p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><i> ibrav=
4
</i></p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><i> A=9.4851, B=9.4851, C=8.7867,
cosAB=-0.5, cosAC=0.0, cosBC=0.0</i></p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><i> nat=19 , ntyp= 3,</i></p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><i> ecutwfc =70, ecutrho= 840, </i></p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><i> occupations= 'fixed', </i></p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><i> nbnd= 100 </i></p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"> </p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif">The vc-relax ran successfully and I got the following
output:</p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"> </p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><i>Final enthalpy = -5322.7186767755 Ry</i></p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><i>Begin final coordinates</i></p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><i> new unit-cell volume
= 1536.19292 a.u.^3 ( 227.64030 Ang^3 )</i></p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><i> </i></p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><i>CELL_PARAMETERS (alat= 17.92424134)</i></p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><i> 0.638651125 0.103631841
-0.047929083</i></p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><i> -0.235833337 0.630643088
-0.049740867</i></p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><i> -0.043220738 -0.085864416
0.635634338</i></p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"> </p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif">Here, the output cell_parameter values are not consistent
with the input. I assumed it as ibrav=4 (hex or rhombohedra), but if I use the
output cell_parameter and calculated the final value (using the vector formulas
for ibrav=4 from pw.x documentation) for lattice constant ‘a’, I will get
different values from different vectors. So, my question is how do we analyse
such a system in which we give certain crystal structure as an input and the
vc-relax runs successfully (<b><i>does not crash</i></b>) and give an output
which isn’t consistent with the input crystal system? Can I accept the results
and carry on further because the vc-relax did not crash meaning that everything
is fine?</p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"> </p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif">Please help me in this regard.</p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"> </p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif">Kind regards,</p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"> </p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif">Bharat Thapa</p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif">PhD student</p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;font-size:11pt;font-family:Calibri,sans-serif">UNSW</p></div></div>
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