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<p class="MsoNormal">Prof. Blaha,<o:p></o:p></p>
<p class="MsoNormal">I apologize for not noticing the exceeded size limit of the email.<o:p></o:p></p>
<p class="MsoNormal">Thank you for your comments, especially on calculating the low-symmetry structure in high symmetry.<o:p></o:p></p>
<p class="MsoNormal">Sincerely,<o:p></o:p></p>
<p class="MsoNormal">Ken<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><b><span style="font-size:12.0pt;color:black">From:
</span></b><span style="font-size:12.0pt;color:black">Wien <wien-bounces@zeus.theochem.tuwien.ac.at> on behalf of Peter Blaha <peter.blaha@tuwien.ac.at><br>
<b>Date: </b>Monday, November 14, 2022 at 3:29 AM<br>
<b>To: </b>A Mailing list for WIEN2k users <wien@zeus.theochem.tuwien.ac.at><br>
<b>Subject: </b>[Wien] ,IRelast: incorrect structure for e=0.3 in C44 for TiO2<o:p></o:p></span></p>
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<p class="MsoNormal">Your email must be smaller than 40 kB !!!!<br>
<br>
A couple of comments:<br>
<br>
Very small distortions are always problematic. When do you consider a <br>
certain symmetry fulfilled ? Due to the limited digits of certain <br>
numbers rounding problems (or factors like sqrt(2), or cos(45), ... may <br>
cause such rounding problems, which later on cause problems.<br>
<br>
I'm not surprised to see energy-jumps when comparing energies from a <br>
tetragonal case with an orthorhombic one, where the lattice vectors have <br>
been rotated. Such calculations would require "fully converged" meshes <br>
(k-mesh, FFT mesh,..). You should do the "high-symmetry" case also in <br>
the low-symmetry structure. For this, you have to initialize a <br>
low-symmetry distorted structure and AFTER init_lapw, change manually <br>
the lattice parameters such that you obtain the high-symmetry case. Do <br>
NOT rerun init_lapw afterwards.<br>
<br>
In essence: when symmetry (or better: the bravais lattice) changes, you <br>
should either not include the e=0 case in the analysis or run the e=0 <br>
case as I indicated above.<br>
<br>
PS: With a struct file, maybe the developer of IRestast could play <br>
around ....<br>
<br>
Best regards<br>
Peter Blaha<br>
---------------------<br>
Von:<br>
"Park, Ken" <Kenneth_Park@baylor.edu><br>
Datum:<br>
13.11.2022, 16:18<br>
An:<br>
"wien@zeus.theochem.tuwien.ac.at" <wien@zeus.theochem.tuwien.ac.at><br>
<br>
Dear Wien2k developers and experts,<br>
<br>
I have been using wien2k 21.1 and IRelast package to calculate the <br>
elastic constants for rutile TiO2 at pressure =0.<br>
<br>
When I used a small strain such as e = 0.3% was used for C44 (monoclinic <br>
distortion), the script generated an incorrect structure causing a <br>
crash. Below is a top portion of the structure with beta not equal to <br>
90, for which wien2k expects alpha=beta=90.<br>
<br>
<br>
<br>
[parkk@login001 tio2r]$ head -10 tio2r.struct<br>
<br>
TiO2 <br>
<br>
<br>
CXZ LATTICE,NONEQUIV.ATOMS: 4 12 C2/m<br>
<br>
MODE OF CALC=RELA unit=bohr <br>
<br>
<br>
12.390517 13.568280 12.390517 90.000000 90.000562155.460807<br>
<br>
ATOM 1: X=0.00000000 Y=0.00000000 Z=0.00000000<br>
<br>
MULT= 1 ISPLIT= 0<br>
<br>
Ti1 NPT= 781 R0=0.00005000 RMT= 1.78000 Z: 22.0<br>
<br>
LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000<br>
<br>
0.0000000 1.0000000 0.0000000<br>
<br>
0.0000000 0.0000000 1.0000000<br>
<br>
<br>
<br>
The structures with e >= 0.5 seem working all right. Could you look into <br>
this issue?<br>
<br>
<br>
<br>
I also have been getting negative values of C44 and C66 in higher order <br>
fit (4). So, initially I thought I needed higher rkmax in calculating <br>
those elastic moduli, but then, I found out that the energy at e=0 <br>
remains higher compared to those up to about e < 1, despite of using <br>
rkmax up to 10. (See the attached figure for C66.) With more data <br>
points, it becomes clear that it is due to the e=0 data point lying <br>
above the neighboring points by about 1.5 mRy. I believe that different <br>
symmetry constraints are responsible for the energy discrepancy between <br>
e=0 (tetragonal) and e != 0 (orthorhombic ) as the distortion for C66 <br>
lowers the symmetry from the tetragonal to the orthorhombic. This would <br>
explain why I see a similar energy jump at e=0 also for C44, which <br>
involves the deformation from tetragonal to monoclinic whereas the other <br>
three distortions c11+c12, c33, and czz (all tetragonal) don’t show <br>
such. So, I think that in the calculation of the elastic moduli with the <br>
distortions involving symmetry change, the e=0 structure should not be <br>
included. Could you comment on this?<br>
<br>
<br>
<br>
If it may be convenient for you, I will be more than happy to provide <br>
you the structure and outputeos files.<br>
<br>
Respectfully,<br>
<br>
Ken Park<br>
<br>
-- <br>
--------------------------------------------------------------------------<br>
Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna<br>
Phone: +43-1-58801-165300<br>
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